I'm trying to use RTA to overwrite some asm permanently, and change it in the exe. When I get to a certain part of the code, RTA either crashes, or says "Access Violation" and I have to close the whole thing via task manager.

I'm using this version of RTA: http://www.openrce.org/downloads/details/170/RTA

Not sure what your issue with RTA is, but you can get the same functionality with OllyDbg

Here are the steps:
- open the file in ollydbg
- right-click on code you want to modify -> 'Assemble'
- put your replacement instruction (rinse and repeat)
- when done, right-click in CPU window -> 'Copy to executable' -> 'All modifications' then select 'Copy all'
- In new window right-click -> 'Backup' -> 'Save data to file'
- Done

Thanks, that worked.

even simpler, you may use hiew