It doesn't seem like you're working on top of the latest dev build, Steve. Please make sure you are before pushing changes (and also that you push the changes into development as well).
I haven't been. I've been working with the 64-bit version, which hasn't been updated for a few months now. To be honest, I'm not certain if I'd prefer to update QB64 to add $REPLACE as a standard command for everyone, or else make it a script which someone can use to add the capability to their version if they desire. (Much like my AutoSave script does which alters QB64 to save the current IDE program to a time stamped BAS file every XX number of minutes.)
If an user has to install it, they're a lot less likely to misunderstand what it does and how to use it.
I'm thinking easiest solution is to change it to be called '$REPLACE, so users without the mod *CAN'T* be affected by it, and then have a small BAS file/EXE where somebody could use to update the ability into their personal version, if they choose. I'm thinking that'd probably be the easiest way to add functionality, while minimizing misuse/misfunctionality, as much as possible.