Yes you can defiantly do that, actually I've done it before. They really don't care as long as they're getting money. I mean you can pay twenty dollars in cash ten dollars with a credit card and another ten with a check, they really don't care.
Yes, you most definitely can. Split payment is offered at any retailer that has accepts credit or debit cards. I have done this many times; but I have learned that keeping to much cash on you can lead to trouble.
At Wal-Mart all you have to do is pay the cash first and then use the card last. You do not have to say anything in the beginning except for communications. Technically you are o.k. to wait until the cashier hits "total"
Yeah, it's a split payment. Most retailers who have a credit card machine can do it, just make sure to let the cashier know before she's starts ringing it up.
Shouldn't be a problem. Pay with the cash first, it is easier on them to put in the cash they give you and then just run the balance on the credit card.