Two things here: You will have 6 months from the official date of withdrawal for a grace period on loans that have never used the full grace period; any loans for which the grace period is expired will go into repayment as of the date of withdrawal.
You do not just get to keep your loans. The school has to do a Return of Title IV Funds calculation. Some funds will be returned, based on the amount you have “earned” as of your date of withdrawal. You may very well end up OWING your school. In addition, your loan eligibility at the new school will be limited by the dates of your current loan disbursement (if the loan period of the current loan is Aug-Dec, you may not be able to borrow again until Jan). Please talk to your financial aid office to find out how your plan will actually play out.