I think in many cases you can. If you replace with compatible cells, you can keep the BMS. For some batteries there are reverse-engineered or alternative BMSes.

I think in many cases you can. If you replace with compatible cells, you can keep the BMS. For some batteries there are reverse-engineered or alternative BMSes. However, cells need careful soldering, and the BMS must be working properly to prevent overcharging and overheating. Mistakes can cause nasty and expensive fires, so it's not a DIY job for anybody.