It is possible, yes.
It will, however, require a complete reinstall of your cluster into a Full HA setup.
I'm fairly certain migrating distributed TO a Full HA setup won't be possible without having to resort to using an API-based solution like https://community.checkpoint.com/t5/API-CLI-Discussion/Python-tool-for-exporting-importing-a-policy-...
Migrating from a Full HA to a distributed environment will present its own challenges, since I'm not sure we have a supported method for doing so (this procedure only applies to R7x versions: https://support.checkpoint.com/results/sk/sk44201 )
In short, I would strongly advise against doing this.
I would consider looking at Smart-1 Cloud instead or maintaining your existing external management server.