If both the source and target classes are yours, I don't see a big problem in reblessing between them. Just make sure you don't carry any unwanted internal state from the previous class.
On the other hand, if you're using Mo*, there might be cleaner ways how to achieve the same, e.g. applying roles to an instance at runtime:
'Moo::Role'->apply_roles_to_object($self, $read_only_class);
It reblesses the object behind the scenes, anyway. To disable the writers, you probably need to around them.
($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,