Okay, I see what you mean now. I thought you meant you'd need 50BI for the next level before taking shots/moving up. Interesting. I might shot 200NL at a 6k bankroll (~5BI).
That's exactly what I mean.
You just need the discipline to drop down immediately if you go under 5K again. If you lack that discipline, then you really should grind to 50BIs for the next level before taking shots.
The irony of the situation being that if you lack the discipline for the former, you'll lack the discipline for the latter.
You could also use a changing system where it's 50 BIs for the lower stakes, but increases as you move up. Any system is fine. It just depends on your own preferences.
As long as you do in fact use a bankroll management system, all is good. BRM is very important but BRM can be handled in many different ways...