Rebuilding Makita NiMH Battery with Cells of Bigger Capacity. Will it Charge Properly on the Old Charger?
NiMH chargers terminate the charge based on dV/dt flattenings, with temperature as a backup/safety measure. So your old charger should charge the new cells just fine, only a bit longer.

However, professional power tools use battery cells that don't have an impressive capacity not because they want it cheap and low-grade, but because they want to have high discharge rate and drive the tool's motor hard. Unfortunately, high-discharge cells do have a somewhat smaller overall capacity, this is a design trade-off. So you need to worry a bit and better check if your new high-capacity cells have good discharge rate and can drive your tool to full design capacity/torque.