The dividing point between the so called hi and lo band is ch35. First this applies only to Futaba Rx's all the other brands do not have this restriction. Unless you have a Tx with a removable RF module then you cannot change the channel (crystal) yourself without a retuning. However you can legally change the crystal for another channel in your Rx legally. So what Futaba is saying if your Rx was originally on a channel below #35 then you should only change that Rx to another channel that is also below #35 unless you send it in for retunning.

John