Currently it could be done by opening resource in editor. While it's opening, wxSmith rebuild source code and update it if source has changed.
Updating whole project could be made by clicking all resources one after another in resource browser (pretty fast) and then Ctrl+Shift+W (even faster

). Still hand-made solution but works

It could also be implemented while opening project but it may slow things down (it would require loading all wxs/xrc files, generating sources and working on files). Since loading speed is critical for some coders, it should be optional.
But that's good candidate for feature request (f.ex. some option in either wxSmith configuration or project options or both of them and some Regenerate on demand feature

). I would have to measure some real timings to have some basis, but now few other things have higher priority.
BYO