NT has converted a rather feeble dynamo lamp on Granville the shopper with the innards of a head torch.
There might be those who'd consider it sacrilege, but if you wanted a vintage bike with a vintage lamp, but actually wanted to use it, then I don't see the problem with upgrading it. It could probably be done with minimal damage, if one was careful.
Perhaps if it was the last of its kind, it should be preserved, but otherwise, why condemn it to being feeble when it could be useful.