This has been discussed with Doug on Thomas Tuesday Livestreams, the market and interest may be there, but the fact is that the faces on the locomotives are not meant to be removed by the average consumer. There is no designed way to remove them. It is quite easy to damage the products by removing the faces and- depending on the engine- the eyes come out with the face. which makes them incredibly fiddly to refit. There will be no alternate face options unless the loco toolings themselves are updated to accomodate the feature. I recall talking with Doug about this to which he said something along the lines of "we would end up with many broken thomas' in the repairs department."

Niche modifications like this are well covered in the fandom already too. there are many options to purchase STLs or face prints from lots of different individuals. Kato has recently released a thomas face and while I believe its only available in japan, the fan ones are still of higher quality. We are now at the place where scans of actual prop casts exist digitally and for free! https://x.com/thomasmodeller/status/1920301786302177469?s=46