There is no legal requirement to have the number stamped in following a theft. If you decide to do it yourself or get someone to do it, you could be letting yourself in for a problem, unless it is done to factory standards. As we all know, 4x4s are prime target for vehicle crime. Therefore, Police tend to stop and check a large proportion of 4x4s. Imagine how much your suspicions would raise if you were a policeman and you stopped a 4x4 with a stamped in number that wasn't exactly as it should be. I realise it is explainable, but, probably not at the roadside in the middle of the night to a suspiscious bobby just doing his job.
Just my opinion but I wouldn't bother. Just get the vin plate sorted and leave it at that.
Hope this helps
Graham