Sure, i see no problem on that.

* Sapphire nor Lynx use the wallet.dat. They both interact with the daemon (the real wallet) and the daemon uses the wallet.dat

So lets say you download lynx, and download the daemon trough lynx.
Then start the daemon trough lynx, the daemon creates the wallet.dat file.

Later on you download sapphire, then start sapphire.

Sapphire automatically detects if there is a daemon present, since you already downloaded the daemon trough lynx it will start that same daemon.
And the daemon will load the wallet.dat file that was created earlier

That's why you can use sapphire and lynx at the same time, even have them running at the same time.
as long as the daemon is new enough that sapphire can actually interact with it

Anyway, just be sure to have several copy in safe places of your wallet.dat "justincase" something sometime goes wrong
(Never hurts to remind that) 

Also i would invite you to join our Discord ("Headquarters") https://discord.gg/BYBhQVq
and Telegram channel https://t.me/joinchat/F_LCJQ0vhFFknOSMgxHPAw
(in case you didn't yet)
as it may be quicker for you to get any help you need

*Kudos to Pem199 for the great explanation regarding to Lynx and Sapphire as GUI and how they relate to daemon, the "real" wallet. Unsure if he's around here, but he's in our Discord