I think its personal preference whether a person changes a horses name or not. I have just been through this with my mare and we have just bought another today that will also be having his name changed.
My mare was possum
and I changed it to gypsy. The gelding came from the same fella (he's finally selling his horses rather than just not feeding and looking after them) and we haaaaaaaaaaate his name. His name is currently jarred
Both horses were taught to come to a whistle. Neither of them respond in any way, shape or form to their names. Basically, we have two horses who needed a new start and a new name is perfectly acceptable. We are also thinking of another name for the sb we have bought but can't get until the flu ban is over. His name is cougar. Again, not a name we are comfortable with. We see little issues with him as he doesnt respond to his name or a whistle lol
I personally believe that it doesnt matter what the horses name is when you get it, it WILL get used to the new name. It will just take longer in some horses than others. Mostly I think they respond to the sound of their owners voice rather than the actual name they are saying.
I think touche' is a wonderful name and if you feel happy and comfortable with it, then go for it :)