Replace bath tap inner valve, combi boiler? Worcester heatslave 12/14?

Hi, I want to replace a loose tap inner valve, Can I turn off main water supply to house with a combi boiler? Then run off hot water the same way as with the older type of water system?
Once I have replaced the tap valve just turn boiler and water back on? Or do I need to re- pressure combi tank back up or any other complicated procedures?
I dont want to damage the combi in any way and I have no experience with combi boilers. Its a Worcester heatslave 12/14, approx 7 years old.
Any advise would be greatly appreciated.
Thanks.