@Jonas ************
, Actually, for OP's particular case, when you already are seeing to transfer stamps soon, I recommend applying for a re-entry permit at the immigration office where you apply for an extension.
You may need to apply for transferring stamps separately for an extension and re-entry permit if issuance offices are different. I.e, need to transfer the extension stamp at the local office and re-entry permit one at the airport office.
But where to apply for a re-entry permit is a bit out of the topic of OP.