Unsyncing from Steam? (Steam Overlay Problem)

Hello. I'm Kitorin.
For a year now, I haven't been able to make purchases on Spiral Knights because I cannot use the Steam Overlay. (The game turns off every time)
Since I've dont over 1000 attempts to try and fix this, and none of them work. I'm at a last resort.
Is it possible to unsync from Spiral Knights on Steam and just become the Spiral Knights Client?
I've heard there wasn't a way to,but if there is, I would love to unsync it, just so I'll be able to purchase the much needed Crystal Energy.
(And don't tell me I can use the website to make CE purchases, but I've checked and it only leads me to a webpage on how to purchase CE using the Steam Overlay that I can't use)
If it is possible, I have a few questions about it.
-Will I still be able to use my Main Knight. I've been using it for 3 years, and i would love to still have him.
-I've made my Account on Steam first, so would it sill be possible to use that same account?
- If and when I get a newer computer with a better graphics on it so Steam Overlay can work without issues, would I be able tore-sync my Spiral Knights Account with Steam again under the same Steam account?
If it is possible, please let me know and I will do the steps on what i must do.