One great way to introduce default values in Biml would be variables in include files or code files for example. But depending on what you’re trying to achieve or at what point you realize it, it may already be causing some extra work.
For example: You have a couple of diffent ways to create a dataflow task but in the end, they should all share a property like DefaultBufferMaxRows.
In BimlStudio, you could make use of a transformer, but these are not available in BimlExpress.
As a bonus, this is a bilingual post on two fronts, so you can pick up a little English-German translation as well as a little VB.Net-C# translation.