I am inquiring if any Bank has written in their REG CC policy that $5,000.00 amount is now in play for $20,000.00 over hold amounts only.

I am wondering even if this action is allowed.

If you make it a standard practice to hold all checks over $20,000, then your funds availability policy would have to be amended from a case-by-case disclosure to also disclose mandatory holds for checks for more than $20,000.