changing bin code a bit

Question

If in exe (written in c++) file in .text section I'll add instruction like push eax; pop eax; I mean something what won't change anything. Will this program work properly or everything would get crashed ?

Answer 1

I guess it depends how you add these instructions. If you insert them in the file you risk breaking offsets in both the code and its executable container

Answer 2

It will probably cause problems if you insert it at a random location in the code, as it will displace other code addresses after it. If you append it to the end you'll probably be OK, unless the code has internal checks for tampering (CRC, digital signature, length check, etc).