This is from Brett on the official Altium forum. What you do is to set up a custom toolbar button and copy the data in that he shows.
Then when you are actively on one of the layers of the mechanical pair (the tab is selected on the tabs along the bottom) and you run this tool bar button you just created, it will separate the pair but NOT delete any primitives (lines arcs, etc) on those layers. It works like the Old Altium AD17
Post ID: 779076
Right click on the toobar and select Customize
Create or copy a toolbar button and set:
Process :ScriptingSystem:RunScriptText
then paste the below text into Parameters:
Text=Var B;C;I;P;M; begin B:=PCBServer.GetCurrentPCBBoard;P:=B.MechanicalPairs;C:=B.CurrentLayer;for I:=1 To 1024 do begin M:=LayerUtils.MechanicalLayer(I);if P.PairDefined(C, M) then begin P.RemovePair(C, M);ShowInfo('UnPaired Mech Layers :' + Layer2String(C) + ' & ' + Layer2String(M));break;end; end;B.ViewManager_UpdateLayerTabs;end;
Youcan then find some icon to use or just leave it as a text on the toolbar
This will unpair any selected mechanical layer with NO loss of primitives.
Thanks Brett!!!