It's built in now, but doesn't work exactly the same.
You can use the [set [text] for [text] to [anything]] block from the data structures extension to modify any of the values you've set up for your dialog. (Don't confuse this block with the [set [text] for [anything] to [anything]] block.)
set [property identifier] for [structure name] to [value]
ex: set [msgBounds] for [Default Style] to [rectangle x: [10] y: [10] w: [400] h: [180]]
It's a little annoying right now, but you have to open the structure definition editor to actually see what the property identifiers are. They have to be valid variable names, so usually they'll be similar to the property label but with no spaces and camel-cased. For example: Default Type Sound --> defaultTypeSound.
You also have to put an object of the correct value into the last field. You can also see what value each property expects by looking at the structure definition. In the above example, that's a rectangle.
I think Stencyl should have you pretty well covered for most types of data. There are a couple types specific to the dialog extension though, and I haven't created blocks for them yet, so I'll cover them here.
Ratio Point: this is point that has both an absolute x/y component as well as a percentage, and it's used for positioning certain elements relative to a set of bounds. For example, a window's "position" field is a Ratio Point, so you could place it at (0, 100% - 100): The left of the screen and 100 pixels from the bottom.
code: new scripts.ds.dialog.RatioPoint(x value, x percent, y value, y percent)
ex: new scripts.ds.dialog.RatioPoint(-100, .5, -40, .5)
That would be (50% - 100, 50% - 40)
There's also RatioInt which is similar to RatioPoint, but it's not 2-dimensional.
code: new scripts.ds.dialog.RatioInt(value, percent)
example: new scripts.ds.dialog.RatioInt(-100, .5)
