No, that's not possible; you'd have to uninstall.
I mean, of course you could manually remove the relevant registry keys to prevent the processes from starting, but first it's not everything (there are other things being loaded, e.g. drivers), second they would most likely come back during program updates (and possibly other operations), third there's no point in having Avast in that state on your machine (I would say it could cause more harm than good) - so uninstalling would be a safer option.
