You should be able to change country. I haven't found anywhere in the past 10+ years where Apple says there is a wait time for changing countries.
The 90 days refers to being able to use certain services, as outlined in: View and remove your devices that are associated with your Apple Account for purchases - Apple Support
Apple has regional licensing for media and content. The system is not designed for short-term changing of country. You can contact Apple and ask them to change the timing on your account but realize they may just say you have to wait the 90 days. In future, don't change country settings unless you are really going to stay somewhere for a long time.
This support article has various country telephone numbers for contacting Apple for support and service ➔ Contact Apple Support - Apple Support For some countries look under “Other” listing at the end of each region. Not every country has telephone support. You may also find that you cannot get in touch with somebody from Apple if you are no longer in the same country as that to which your account is set. The telephone numbers tend to be country-specific and won't work for callers outside that country.