Jongware, Furry & CW, you're all right!
Funny: with Transform Panel's 2 options: Dimensions include (or don't include) Stroke Weights; and Stroke Panel's 3 options (Align Stroke Center, Inside, or Outside)… there are 6 possible settings.
All of which are illustrated here:
https://hylandbaron.com/images/…..stroke.jpg
(You might want to drag the image to your desktop to read the captions, as browsers reduce the image. It's only 209k, but it's 800 x 1000)
The green boxes (2 & 5) do what I want. Funny: the “Align Stroke Inside” option makes the Transform Panel setting moot.
CW, you ID'd the grrrrrrr factor:
“i don't know how to make “align stroke to inside” a default though, which would save the process of fixing this every time.”
Once you change an object's stroke to 0, the Stroke Panel automatically switches back to the (teeny tiny!) “Align Stroke to Center” setting. (Pink boxes, 1 & 4)
So when you add a 6 pt rule, the object is suddenly 6 pts wider and taller.
And depending on which of the two Transform Panel options are selected… the x,y,w,h fields in the CP may or *may not* change / alert you.
If you're on “Dims incl. Stroke Weight”, then at least the object's dimensions will change in CP, which is better than *no* red flag at all.
I tried to figure out how to circumvent this with Object Styles, but there's no way around the stroke setting reverting to “Align Center” once you set the stroke to zero.
*Thanks* guys for helping me figure out what was at the bottom of this!