Callbacks are never fired on the cellName changing (there's a CCR for that). Some PDKs workaround this by making it that the cellName can't be edited.
The fundamental problem is that there's no way in CDF to specify a callback on the cellName - because it's not a CDF parameter. Even if there was, it is more complicate than that - if you have CDF parameters with defaults which different between devices, and they have storeDefault=yes, then they'd need updating too.
I have the same issue. I think in schematic properties for it's possible to somehow override the callback of the cellname field by accessing cdfForm ... but I'm not sure if this is safe;
Anyhow .. beeing interested in a solution for this: how could I make libname/cellnameto be readonly ?
There's a private way to do this - so that it also disables it in the property assistant and canvas label editing - but there's an enhancement request, CCR 768873, for a clean, public way to do it in property editor, property assistant and canvas labels.
Please contact customer support and request an enhancement and they can then duplicate the request with this CCR.