Is there any reason why a item, lets say pre-war money would not be seen as a salable item ingame after its resale value has been changed/edited ?

No.

So, have you (or anyone else) tryed changing the value of any items and were you still able to sell them ingame ? There are items iv changed sell values on and for some reason the game doesnt see it as a salable item.

You can't sell people things they own, so if you've walked into a shop, picked up some of the stuff you've changed the values of and tried to sell it to the shop owner they won't buy it.