Spoofing by patching the target app requiring GCM, instead of microG itself?

Hi, microG works perfectly on my previous phone with LineageOS and haystack patch. However I recently changed to a new xiaomi mi6 without GMS preinstalled, and I do not intend to root or use a 3rd-party ROM.

Correct me if I'm wrong, every app that utilize GCM come with a little piece of google sdk code inside their apk. This piece of code would be very similar across all apps, and it is exactly this code asking for the signature of microG and check it against the correct one(which must be a static value inside the code). If we can decompile the and patch the target app (for instance, search/replace the static signature with microg's sig, or something more straightforward), repackage and install it, it should work with microg. The result apk will have different signature, but it can be managed.

I have over 100 app on my phone, but the ones that really need with GCM are less than 10. If we can automate this repackage process(termux have apktool so this process could be done on android), we can enjoy GCM without root/spoofing/bloatware, on any phones.

I would like to try this idea first with the search/replace trick, but I don't know google's original signature, so I can not search/replace. Could anyone give me the google signature that need to be replaced?

The issue names no repository file, test, or entry point; it proposes patching target APKs with apktool from Termux rather than changing GmsCore. First determine whether that approach is in scope and locate any existing signature-spoofing documentation; done would require an agreed, reproducible implementation and validation across affected apps.