I`d leave the knots as they are .....hair is sometimes colored using fabric-dye, and bleach will have no effect on it apart from weakening the hair and leading to early / profuse shedding-out of the hair.
I too was a victim of these hair-clubs, including having hair added to an aging system --total waste of time /money .....the ` new` hair hadn`t oxidised [obviously] as it was new ..the existing hair was looking ` tired` from sun -exposure /washing etc. ...the difference was obvious.... the old hair continued to shed out, so as far as I`m concerned, it`s a bit of a con-job having hair added to an old system..just costs you money ...money which would be better spent on a new system.....for the [reasonble] cost of a lace system from Toplace, it`s better to just order regularly ..always have a ` spare` system to hand in case of some type of mishap with the one you`re wearing, or sudden shedding sets in..... I recently received two systems...had the second one cut-in today ...won`t begin wearing it for another week or two [need to leave it ` settle` ] but have just ordered two more from John ..... I`ll have them here /to hand ``just in case`` ! I get quite a few months from mine, but it can vary a lot from one person to another ---there are many ` local` factors at play so it`s not possible to give an exact figure on how long you might expect your system to last for.
Hope your new system looks great after your cut-in !