Some people have been able to do this, though I have no idea if there is a limit. Others have found that their card doesn't allow this, so you would have to contact the credit card company to see if they allow this.
Expect that at some point they will return the funds to you if you try this and keep the excess funds on the card before3 making the purchase. You will have to contact the company to see what their timeline is.
You don't want to be hit by the vendor with a declined card charge if you you exceed the limit, or wait a day too long.
You may be able to get a temporary or permanent credit limit increase. I have done this in the past. It is also possible in some cases to split a large payment across multiple cards, but that would be hard to do if you are making the purchase online.
You may get a discount if you pay cash or with a check, that discount can be larger than the cash value of the points.