When I was a kid several of the less scrupulous importers did that very thing in order to enhance the "salability" of the surplus S&W, Webley and Enfield revolvers they were offering. Ditto for some "Lend Lease" S&W's and Mk.VI .455's to .45 ACP.
As has been said, it's not a good idea! Even with factory-loaded, standard pressure .38 Spl. ammo bulged and/or split cases were common and accuracy abysmal. Since standard SAAMI average pressure specs for .45 ACP ammo are pretty much the same as for "proof" loads for .455 Webley ammo, you can see why that one wasn't such a nifty idea either.
Now that the .38 S&W cartridge has gotten something of a new lease on life from the Cowboy Costume Show bunch the proper cases are much more readily available than formerly, and even commercially cast bullets of the correct size. Why take unnessary chances? Especially with an irreplacable, historically interesting artifact.
FWIW, I owned a surplus .380/200 Webley in my youth. In fact, I became a reloader in order to be able to shoot it regularly. In a pinch, standard swaged or soft-cast 148 gr. HBWC's over about 2.1 gr. of Bullseye can be used successfully and usually give acceptable plinking accuracy.