I wouldn't recommend you to stop avast services - mainly the iAVS4 update service - without it the updates won't work anymore (unless you're logged on as a admin, which is, say, not wise
Regarding the other comments: update does perform full 'repair' operation, what means it sets all parts (including residents) to their default settings.
If you stop your resident task, there will be only icon on the taskbar, it should not interfere with other av products.
Avast currently doesn't support non-resident mode of operation. Until this changes (you may request it in wishlist topic), setup will do what it does.