Yes, it is possible to switch to a different version of Bitcoin Core while using Umbrel. Here are the steps to do so:

1. Connect to your Umbrel node via SSH.

2. Navigate to the directory that contains the Bitcoin Core data by running the command: `cd /home/umbrel/umbrel/bitcoin`.

3. Stop Bitcoin Core by running the command: `sudo systemctl stop bitcoind`.

4. Find the version of Bitcoin Core you want to switch to by running the command: `sudo apt-get install ` (replace `` with the version you want to install, for example, `bitcoin=0.22.1-1`).

5. Install the new version of Bitcoin Core by running the command: `sudo apt-get install ` (again, replace `` with the version you want to install).

6. Restart Bitcoin Core by running the command: `sudo systemctl start bitcoind`.

After completing these steps, your Umbrel node should be running the new version of Bitcoin Core. Keep in mind that switching to a different version of Bitcoin Core may require you to re-sync the blockchain from scratch. This can be a time-consuming process depending on the size of the blockchain, so be prepared for that possibility.

I hope this helps! Let me know if you have any other questions or concerns.