I'm not married to this idea of reusing variables, but I'm still not quite convinced it's the wrong idea either.
I'm not entirely sure of what's your positive reason for reusing variables, though. I find Francisco's current solution reasonable. I had a few comments on some specific details, but the general architecture makes sense. I'd say that native behavior makes it rather natural to think a SM1-3 sampler as, secretly, a SM4 sampler plus a resource, so the transformation Francisco is introducing doesn't look hacky. OTOH using the same variable object for two different things doesn't feel very natural. I'm sure it can be made to work, but I see little value in reconsidering previous design choices for what doesn't really look like an enhancement in itself. Could you please explain what you like of your proposal?