Is there a way to set an absolute value when weight painting for an armature in 2.81a I am trying to add weight paints to many precise points of a mesh. There is the obvious add or subtract value but I'm trying to find one that paints an absolute value. Like if I want a vertices to be a 0.5 weight regardless of if it's already a 0 or a 1 before painting that point. Or if I want to make a strip of a value of .75 then I can set it and paint the strip rather than add and subtract until I am close enough.
Set the Weight to the desired value, the Blend Mode to Mix and the Strength to 1. That will erase everything above your brush and set it to the desired weight.

Alternatively, you can go in Edit mode and select the vertices you want to "flatten" to a value. Then go to the Object Data Properties panel ; under Vertex group, select the desired group, set the desired weight, then hit Assign.