While patching yourself is easy, one has to make sure to have the correct unpatched Rom file. With patch files like in .bps format this is not a concern (in the sense that it contains an internal checksum and the program will prevent from applying it to the wrong Rom), but with the other common format .ips there is no check in builtin. This is just a heads up warning to check and make sure to have the correct Rom file. Filename alone is not sufficient for identification.

My goto patcher is https://www.marcrobledo.com/RomPatcher.js/ . I recommend on the bottom page to click the "Settings" and enable option "Fix ROM checksum".