Adding my own assembly code to x64 .exe

Question

I have assembly code like this:

   142cccc0c c7 43 18        MOV        dword ptr [RBX + 0x18],0x4000
             00 40 00 00
   142cccc13 e8 a8 79        CALL       FUN_141a845c0                                    undefined FUN_141a845c0()
             db fe
   142cccc18 8b f0           MOV        ESI,EAX

It's a part of some function. I'd like to add my own function call after that and pass the return value (I guess it's stored in ESI).

I saw this: adding instructions in IDA, but I'm wondering if there's any easier method?