Removal of the 'use 5.012' (or changing it to 'use 5.010') means that the code isn't protected by 'use strict'. Hence, any further modification of the code is subject to the same dangers any code without 'use strict' is.
In any project where I have a say in coding standards, all files must declare an expected version of Perl 5. That's the only hope Perl 5 has of getting out of the compatibility morass, and it's good discipline anyway.
(I realize that doesn't help when someone changes use 5.012; to use 5.010;, but it's a start.)