Ohhhh tricky disclosures...
So my suggestion is to make the change in the disclosure, but also make the change with your service provider (or internally if you do it that way), to lower the limits for all NEW customers. Most card systems should let you manually change the limits, so it isn't a big deal to do this. That way you make the change, notifying new customers when they sign up... and then make the adjustment for exsiting customers on July 1.
I would caution you about making the disclosure without making the actual change for new customers, because should a card go lost or stolen and should a card not present transaction run through for more than $500... and should some other things happen which makes the customer want to sue your bank, you provided an inaccurate disclosure, which may or may not get you into trouble legally...
Cheers!
_________________________
In life, there is a lot less that could get better and a lot more that could get worse.
MBA Fin/MBS HR
My views only!