DRC error & Constraint manager / Spacing

Hi!

In my layout are a few shapes. Concerning the voltage, 0.25mm spacing is sensitive. I get several DRC errors like this one:

LISTING: 1 element(s)

           < DRC ERROR >

  Class:           DRC ERROR CLASS

  Subclass:        TOP

  Origin xy:       (82.96 10.66)

  Constraint:      Shape to Shape Spacing

  Constraint Set:  DEFAULT

  Constraint Type: NET SPACING CONSTRAINTS

  Constraint value: 0.51 MM

  Actual value:     0.25 MM

  - - - - - - - - - - - - - - - - - - - -

  Element type:    SHAPE

  Class:           ETCH

  Subclass:        TOP

  Part of net name: N18349469

  - - - - - - - - - - - - - - - - - - - -

  Element type:    SHAPE

  Class:           ETCH

  Subclass:        TOP

  Part of net name: N18335736

  - - - - - - - - - - - - - - - - - - - -

I could not find the place, where the actual value of 0.51mm is stored. (Even after watching Module 09 of Allegro PCB Editor Basic Techniques v17.4-2019QIR4.)

I opened Setup / Constraints / Spacing... and typed in 0.25 at Spacing / Spacing Contraint Set / All Layers in column SCS and Row Shape To. After that, all the layers seem flooded with their main colour, no more black inside the outline.
This is because the shapes' dynamic fill is reset and needs update. This can be done via DRC / Display Status / Update all for example.
Unfortunately, this change is one more thing, where Undo is not possible.
Where can I correct the wrong shape-to-shape constraint value of 0.51mm?

Kind regards, Manfred