this is your bible -
https://www.easa.europa.eu/system/fi...u/Part-FCL.pdf
Appendix 3, Part E,
An applicant wishing to undertake a modular CPL(A) course shall complete all the flight
instructional stages in one continuous course of training as arranged by an ATO. The theoretical
knowledge instruction may be given at an ATO conducting theoretical knowledge instruction only.
basically you either do whole CPL training in one school or you can do theory bit in a school that does theory only (such as Bristol for example). That gives you 2 school maximum.
This does not take into consideration where you do your PPL/NR/IR/MEP/MCC/JOC or anything else, it only considers CPL. Generally it would be wise to finish CPL/ME/IR in one place but there are no requirements to do so
Personally I finished my PPL in a club in South Dublin, for Night Rating I went for a different school in Waterford. Tail wheel is just a sign off by an instructor, so it doesn't even involve schools in some cases. ATPL was Bristol, hour building with private aircrafts, CPL/ME/IR will be done in Greece, MCC/JOC either Simtech or Cardiff, haven't decided yet..