How to restrict updating of the currency code field on price list headers

Hello

I would appreciate any suggestions on how to restrict who can update the currency field on an active price list header.  We recently had a mistake by a user which we would like to prevent in future.  They still need to add/update the lines of an existing list, but not update the currency.  The current Note, which displays was not sufficient  to deter them, as they had not realised what they had done.

Would personalisation of the form work, or is this overkill?

Thank you 

Hazel