Cutting the front of the chassis

Technically that constitutes an alteration to the chassis meaning that it should be submitted for a full iva sva or whatever they are called this week. If you are just redesigning the brackets to still hold the original bumper on you might and it's only a might get away with it but it would then be entirely on you if you get caught out in some way. You would be obliged to inform the insurance too and they're going to be adamant that it is correct and to a suitable level of inspection. We had this a while ago and if all you are doing is remaking a bracket even if it's not perfectly like for like that's reasonable, making an entirely new and different bracket to mount a none standards accessory, not so much.