Houserule: what if Warlocks could replace all invocations on level up?

[diplomancer]

I like this. Making invocations more flexible strikes me as value added, since clerics and wizards can change their spells overnight as well ...

Exactly; having at most 8 invocations was alright with just the PHB options; but as more and more invocations get published, the thought of having them mostly unused bothers me enormously; a faster switching rate would see more use of the more niche invocations.