I agree . I almost never shifted the high/low N gear thinking it was the Hydralic 3 pt / mower lift. However when i first started out with hte new
BX24, at first i did what you were saying but noticed a resistance since the BX doesnt like to shift on the fly so i would stop immedaitely. at the top of my head if you are worried about it and want to kinda lock it, why not take a scrap piece of plywood say about 2"by3" and tack it to a scrap 2X4 say about 3 long. Then just slide the plywood between the open slot and the 2X4 will stop lever from moving and the plywood would hold it there with gravity.

I suppose i could put hobble something together quickly and post a pic if you want.