Replacing Files With RPMs

I'm fairly new to making RPMs and I've come across a hurdle my research hasn't answered. I have an RPM that wants to update the contents of a file which is currently also managed by another package. My spec file is simply replacing the old file with a new source file instead of trying to patch with diff. My new package won't install however because that file is being managed by another package. I feel like I missing a key component but the documentation surrounding RPMs is so unclear that it's hard to decipher. Any help would be appreciated.