Is International Micron Extra compeitable to Jotun Seaforce 90 if you apply Jotun seaforce 90 over International do you need any interguard or safeguar Do You have to sand down to epoxy layer?

Yes. Seaforce 90 is a self-polishing antifoul (it is however relatively hard in comparison to Micron Extra) and so it compatible with other self-polishing antifouling. Give the existing antifoul a wet sand and apply Micron Extra. If you go back to the epoxy, or there are areas where the current antifoul is suspect then apply a sealer coat of International Primicon.