It won't necessarily hurt anything, but it's not a good idea (IMHO)... What really matters is the amount of residual oil in the crankcase(this is what actually lubes the engine, about 1/8" of the bottom of the crank wheels is healthy). If you don't have enough residual oil you could\will sieze the piston. 50:1 might be ok, but I wouldn't be the one to find out :)
If I were you I would goto 32:1. It's the proven safe ratio, and the best IMO. You will need to change your jetting when you switch (go richer, I believe). Once you get it jetted properly at 32:1 you can use the ratio to adjust for small changes in temp, altitude, or humidity. More oil (32:1) effectivly leans out your jetting and less oil (40:1) richens the jetting.
www.eric-gorr.com - Has somegreat jetting info.(read it twice, take notes if need be. Knowing how to jet is a VERY good thing!)
www.dirtrider.net/justkdx - Also has some great info
Try using the search function - I believe this subject has been discussed several times. Also, it's motorcycle (one word one 'e') :confused:
Hope you enjoy the "new" ride!! :thumb: