Payment Block in Substitution Rule

I' created a Substitution rule to block particular vendor invoices at callup point 2 when they are entered in the system. At some point in time, I need to unblock these vendor invoices in order to make a payment. When I unblock the invoices, my substitution rule keeps blocking the invoices again. What do I need to do to only have my Substitution Rule work at the time of invoice entry?

Any help would be greatly appreciated.