Well, you can do Cash Out Refinance or HALOC. Once you have the cash, you can do what you like with it. There is no law against that. They will not however give you more than 80% of appraised value (you pay for appraisal) so you get 0.8 * ARV - Loan Balance.
I found it easier to just get a regular line of credit. It has higher interest, but higher line of credit and no upfront fees.