one think i like about Huawei and Honor is they are upfront and transparent about their pricing. all listed here:
https://consumer.huawei.com/my/support/sparepart-price/

labour fee is usually rm60.

as for the reset when changing battery. personal experience is... i was forced to reset. i feedback after that (said pointless to have maintenance mode if it is not used by SC). a friend changed the battery recently and did not have to reset (but had to sign some disclaimer that cannot take action of data loss or sth like that)...