@Chebec Have a read through:
https://docs.netgate.com/pfsense/en/latest/development/patches/custom.html
and the rest of the topic.
If you add a patch, it should detect whether it can be Applied and will or will not show the Apply button, as I recall. There is also a Debug button to test. Normally a patch can be reverted via that button, yes, unless the target file is later changed. (after updating pfSense you would not want to revert a patch and reintroduce a bug, just delete the custom patch)
Note there's a later patch ID in that redmine: 8544b85f8c32d0f180c09a4d0986ac819919bd2b
As long as patches are from Netgate developers I would have no issue installing them. For random patches in the forum I'd be a bit more cautious. In either case you can see the code being changed, in the patch details.
Edit: Marcos M in the redmine is a Negate dev.