It is possible to crunch solo and for a pool at the same time on a single computer, the BOINC client will treat each project/account combination as a separate project and split time between them using normal time sharing rules.
The obvious drawback to crunching pool and solo work concurrently is that you dilute your pool rewards and may not be able to claim your solo rewards if you haven't got enough GRC to stake.
If you do have enough GRC to stake regularly then attaching your projects one at a time in your BOINC client on the same computer as your Gridcoin Wallet could be a good way to transition from pool to solo crunching.
When I went solo I attached a project with a low time share just to test that the Gridcoin Wallet was recognizing my CPID, once I was satisfied that everything was working I detached the pool account and attached my already established BOINC accounts.