cpl(sep) or cpl(mep)

[Mintflavour]

Just looking up for schools on the internet for CPL training and came across the option for CPL SEP or CPL MEP.
At the end of the day I want to get my ATPL frozen with may the possibility of doing some instructing inbetween. What the benefits if any, in doing a CPL MEP compared compared to doing a CPL SEP then doing a Multi before I do the IR.

Also what happens to your licence If I did a CPL SEP then later did a Multi Rating, will your licence be upgraded from a CPL SE to a CPL ME automatically or does it involve more tests?

Any help will be appriciated

Thanks

Mint