Q: Is it possible to edit existing .mst via Wix? I've faced the next problem: suppose we have .msi file which should not be changed and .mst where all the changes should be applied. So, I want to edit this .mst file in order to change registries/icons/etc with Wix DTF.
How I do this via Wix DTF library? Is it even possible? Because I can't find anything in DTF.chm about this issue. There are only ApplyTranform, Generate Transform things.
Appreciate any help, sorry if this question is dumb. 

A: The way you generate a new transform from an existing is to have two copies of the MSI file. 
Using the APIs, apply the transform to one MSI file, then do the SQL updates to that MSI, then use the generate transform call to create the new transform, and that call requires a reference to the original database and the one you transformed. 
So it should be straightforward - maybe the part you're unfamiliar with is the SQL and the APIs used to modify the MSI after applying the transform. And even if DTF did not have every single API (which I think it does) the p/invoke calls to do anything missing are not too complicated.
