Is there a way of rolling profit over into another investment without closing the original trade that created the profit on eToro?

It's not necessary to close an existing trade in order to invest the profit but you can transfer the profits into new positions on your account.

If you have a good feeling about your investment and want to keep holding it, then you do not need to withdraw the money or reinvest it right away - you can wait for a better opportunity, at least until the price recovers from its current level.

Alternately, if you want more immediate access to margins without additional risks, just use this option and get what remains of your original investment. The only condition is that there should be enough funds on the margin account for fulfilling such request of withdrawal beyond the initial margin requirement - otherwise we will cover any active losses with our own capital