It seems like you have to part in the circuit that you want to transpiled and you want to add gate into the middle of the circuit after the transpilation process. If that is the case, then what you can do is to split the circuit into two parts, where you would put the barrier at. For instance:

It seems like your circuit have two parts that is being divided by the circuit barrier, and you want to add gate into the middle of the circuit (after the barrier) after the transpilation process. If that is the case, then what you can do is to split the two parts of the circuit into two different circuits then compose them together after the transpilation process. For instance:

Update:

It seems like you have to part in the circuit that you want to transpiled and you want to add gate into the middle of the circuit after the transpilation process. If that is the case, then what you can do is to split the circuit into two parts, where you would put the barrier at. For instance:

from qiskit.circuit.random import random_circuit
num_qubits = 2
circuit_depth = 3
max_operands = 1 #between 0 and 3
measurement_all_qubit = True
qc_random1 = random_circuit(num_qubits, circuit_depth, max_operands=max_operands, measure= None)
qc_random1.barrier(range(2))
qc_random2 = random_circuit(num_qubits, circuit_depth, max_operands=max_operands, measure= None)
qc_random2.barrier(range(2))
print(qc_random1)
print(qc_random2)

     ┌───┐ ┌────────────┐    ┌───┐      ░ 
q_0: ┤ X ├─┤ U1(2.7235) ├────┤ X ├──────░─
     ├───┤┌┴────────────┤┌───┴───┴────┐ ░ 
q_1: ┤ Z ├┤ RX(0.94815) ├┤ RX(2.0345) ├─░─
     └───┘└─────────────┘└────────────┘ ░ 
     ┌────────────────────┐    ┌───┐     ┌────────────┐ ░ 
q_0: ┤ U2(0.28027,1.7582) ├────┤ X ├─────┤ RZ(4.5689) ├─░─
     ├───────────────────┬┘┌───┴───┴────┐└───┬───┬────┘ ░ 
q_1: ┤ U2(1.6123,1.6426) ├─┤ RZ(6.1746) ├────┤ S ├──────░─
     └───────────────────┘ └────────────┘    └───┘      ░ 

Now, do the transpilation as you would have normally do:

from qiskit.compiler import transpile
provider = IBMQ.load_account()
Circuit_Transpile1 = transpile(qc_random1, provider.get_backend('ibmq_athens') , optimization_level=3)
Circuit_Transpile2 = transpile(qc_random2, provider.get_backend('ibmq_athens') , optimization_level=3)
print(Circuit_Transpile1)
print(Circuit_Transpile2)

               ┌────────────┐                                      ░ 
      q_0 -> 0 ┤ RZ(3.5597) ├──────────────────────────────────────░─
               └┬──────────┬┘┌────┐┌────────────┐┌────┐┌─────────┐ ░ 
      q_1 -> 1 ─┤ RZ(-π/2) ├─┤ √X ├┤ RZ(6.1242) ├┤ √X ├┤ RZ(π/2) ├─░─
                └──────────┘ └────┘└────────────┘└────┘└─────────┘ ░ 
ancilla_0 -> 2 ──────────────────────────────────────────────────────
                                                                     
ancilla_1 -> 3 ──────────────────────────────────────────────────────
                                                                     
ancilla_2 -> 4 ──────────────────────────────────────────────────────
                                                                     
global phase: 0.29049
                ┌───────────┐  ┌────┐┌────────────┐ ░ 
      q_0 -> 0 ─┤ RZ(3.329) ├──┤ √X ├┤ RZ(5.8595) ├─░─
               ┌┴───────────┴─┐├────┤├────────────┤ ░ 
      q_1 -> 1 ┤ RZ(0.071774) ├┤ √X ├┤ RZ(4.6453) ├─░─
               └──────────────┘└────┘└────────────┘ ░ 
ancilla_0 -> 2 ───────────────────────────────────────
                                                      
ancilla_1 -> 3 ───────────────────────────────────────
                                                      
ancilla_2 -> 4 ───────────────────────────────────────

Now, add gates that you wanted to add to the first circuit:

for i in range(2):
    Circuit_Transpile1.h(i)
print(Circuit_Transpile1)

               ┌────────────┐                                      ░ ┌───┐
      q_0 -> 0 ┤ RZ(3.5597) ├──────────────────────────────────────░─┤ H ├
               └┬──────────┬┘┌────┐┌────────────┐┌────┐┌─────────┐ ░ ├───┤
      q_1 -> 1 ─┤ RZ(-π/2) ├─┤ √X ├┤ RZ(6.1242) ├┤ √X ├┤ RZ(π/2) ├─░─┤ H ├
                └──────────┘ └────┘└────────────┘└────┘└─────────┘ ░ └───┘
ancilla_0 -> 2 ───────────────────────────────────────────────────────────
                                                                          
ancilla_1 -> 3 ───────────────────────────────────────────────────────────
                                                                          
ancilla_2 -> 4 ───────────────────────────────────────────────────────────

Then compose them together to formed a full circuit:

Circuit_Transpile1.compose(Circuit_Transpile2, inplace = True)
print(Circuit_Transpile1)

               ┌────────────┐                                      ░ ┌───┐»
      q_0 -> 0 ┤ RZ(3.5597) ├──────────────────────────────────────░─┤ H ├»
               └┬──────────┬┘┌────┐┌────────────┐┌────┐┌─────────┐ ░ ├───┤»
      q_1 -> 1 ─┤ RZ(-π/2) ├─┤ √X ├┤ RZ(6.1242) ├┤ √X ├┤ RZ(π/2) ├─░─┤ H ├»
                └──────────┘ └────┘└────────────┘└────┘└─────────┘ ░ └───┘»
ancilla_0 -> 2 ───────────────────────────────────────────────────────────»
                                                                          »
ancilla_1 -> 3 ───────────────────────────────────────────────────────────»
                                                                          »
ancilla_2 -> 4 ───────────────────────────────────────────────────────────»
                                                                          »
«                ┌───────────┐  ┌────┐┌────────────┐ ░ 
«      q_0 -> 0 ─┤ RZ(3.329) ├──┤ √X ├┤ RZ(5.8595) ├─░─
«               ┌┴───────────┴─┐├────┤├────────────┤ ░ 
«      q_1 -> 1 ┤ RZ(0.071774) ├┤ √X ├┤ RZ(4.6453) ├─░─
«               └──────────────┘└────┘└────────────┘ ░ 
«ancilla_0 -> 2 ───────────────────────────────────────
«                                                      
«ancilla_1 -> 3 ───────────────────────────────────────
«                                                      
«ancilla_2 -> 4 ───────────────────────────────────────
«                                                      
```