I've broken in 3 cylinders / rings on the KLX250S, the stock, 300cc, and 331cc. The first one I did by the manual as much as I could but it's pretty impossible to keep it below 4K. When I did my 300cc upgrade that cylinder had abotu 2500 miles or so on it and it was fine - no evidence of blow-by or anything else which is good indication that the rings were seated fine.

On the 300cc and 331cc I used what is typically recommend for MX bikes after a top end rebuild. Basically just a series of run-in periods which consist of a first run of 0 to 1/2 throttle run up from 1st to 3rd gear and then back down, loading the engine on the way back down for about 20 minutes. Then let it cool down and repeat but the 2nd and 3rd time go to 3/4 throttle and 4th gear. After the 3rd time of doing this, change the oil and filter and call it done. Do that on the road or other hard surface, not sand or soft dirt which tends to overheat the engine easily.