Yes. After supplying your assets, you are able to unselect the asset so that it will not be used as collateral. The opt-out is available in the "Supply" section within your dashboard. Simply switch the "use as collateral" button on the asset you would prefer to opt-out from being used as a collateral.

P.S. You can withdraw your assets without opting out of using them as collateral, as long as those funds are not actively being used to borrow and the withdrawal would cause a liquidation on your loans.