Yes you can rebalance your channels by creating circular onions. That will also cost you routing fees which are currently low.
However in order to get onchain funds you would have to close a channel (or open a channel if you want more liquidity). This means you cannot really swap on chain with off chain funds to provide yourself with inbound liquidity – wich is what loop / submarine swaps are for.
If you use c Lightning you can use the rebalce plugin https://github.com/lightningd/plugins/tree/master/rebalance or the drain plugin: https://github.com/lightningd/plugins/tree/master/drain depending on what exactly you want to do you might have to fork these plugins
