WowAce

Want to both get a Bar and a Line to display shields-overflow to get the following result (manually edited to achieve this)

atm you cant select an used status when creating a new bar, if you give it another status you can then swap status with another bar but it doesnt allow to use the same.

Another possible solution could be to allow Type:Bar to also get a sub Line added at either end of the bar.

Another option is to create an additional multi-bar indicator.

Its anchored to the health bar, so if im not on full health i see absorb to the right of the hp bar and the overabsorb grows to the left, can that be done with an additional multibar?

I dont know because i dont understand your setup very well,i dont even understand why is useful to use the same status twice in two different bars, but if you think that a type:bar  indicator with a line added can fix your issue, then the same is doable with a second multibar indicator, because a multibar indicator has all features of a bar indicator + the posibility to add a line.