OB:S just sets the flag "cannot be visited by any hero". In your case you should replace labs with other object (of any new type, i.e type 63, subtype 3) but with old graphics:
Code:
Additional syntax: You can place an object which functions as object type/subtype but looks like an object type2/subtype2.
If you do so then:
#1 = x
#2 = y
#3 = Level
#4 = Type of object (Format OB)
#5 = Subtype of object
#6 = Type2 of object to look like (Format OB)
#7 = Subtype2 of object to look like
If you use only 7 parameters you cannot set another terrain type and cancel redraw (terrain=-1, redraw=1)
#8 = Terrain type (Format TR)
#9 = Redraw needed (1) or not (0)
And each week loop throw all objects of your type and give mithril to needed players.