DONT CUT IT!!!
Sorry. It'll look really bad when you take it out and you could also cut it wonky and then end up cutting it too short.
After you've worked your horse just pull it a little shorter until you have it the length you want then band it. It will look nice and natural and it won't end up wonky when it's taken out.
I'm on the fence about that, my daughter had a show aobut 2 weeks ago and we spent time banding luna's main.....step back and thought how owlful it made the horse look....(i've ridden and shown english for over 30 years ) so doing this was new to me....best thing to have is a pair of sheering scisors the ones with the teeth in them and cut horazontil to the main.
Um - trimmed the long ends off of my mares mane at a show after braiding it. Took braids out, looked like the haircut I gave my barbie when I was 3 and found scissors near my play area. :/ I was able to trim it up and make it look more presentable loose.