Alternator question

When I bought my car (03 Jetta), the previous owner had put a solid pulley alternator on it. The question I have is can I simply remove the solid pulley and replace it with a clutched pulley or do I need to find another alternator? I have access to the special tools so that is not an issue but I wanted to see if they had different shafts between the 2 alternators.
Thanks

You can change just the pulley

Awesome, thanks for the quick reply.

Is it a 120 amp alternator?

Most likely the PO put in a gasser alternator.