Heh, all that trouble for nothing. Look at this thread in the editing forum. You can have a custom sky for every level, even multiple skies in one level! Just use line special 271 or 272, which will transfere it's upper texture to any tagged sector with F_SKY1.
271 Ext -- Transfer sky texture to tagged sectors
271 Ext -- Transfer sky texture to tagged sectors, flipped
These linedefs transfer wall textures to skies. F_SKY1 must still be used as
the floor or ceiling texture in the sectors for which sky is desired, but the
presence of a 271 or 272 property-transfer linedef can change the sky texture
to something other than a level-based default.
Every sector with F_SKY1 floor or ceiling which shares the same sector tag
as the 271 or 272 linedef will use a sky texture based on the upper texture
of the first sidedef in the 271 or 272 linedef. Sectors with F_SKY1 floors or
ceilings which are not tagged with 271 or 272 linedefs, behave just like Doom.
Horizontal offsets or scrolling in the transferred texture, is converted into
rotation of the sky texture. Vertical offsets or scrolling is transferred as
well, allowing for precise adjustments of sky position. Unpegging in the sky
transfer linedef does not affect the sky texture.
Horizontal scrolling of the transferred upper wall texture is converted into
rotation of the sky texture, but it occurs at a very slow speed relative to
the moving texture, allowing for long-period rotations (such as one complete
revolution per Doom real-time hour).
Effects other than sky-transfer effects are not excluded from the affected
sector(s), and tags can be shared so long as the effects are unambiguous.
For example, a wall-scrolling linedef can share a sector tag with both its
affectee linedef (the one being scrolled), and with the sector that the
latter controls. There is no ambiguity because one effect (scrolling) applies
to a linedef, while the other effect (sky transfer) applies to a sector.
If a sector underneath a special sky needs to be set up to have a different
purpose (for example, if it is a lift or a stairbuilder), then two tags will
need to be created, and the transfer linedef and any scrolling linedefs will
need to be duplicated as well, so that the same effect as far as the sky goes,
is duplicated in two separate sector tags. This will not affect sky appearance,
but it will allow a special sector which needs a unique tag, to sit under such
Animated textures may be transferred to skies as well.
In Doom, skies were flipped horizontally. To maintain compatibility with this
practice, the 272 linedef flips the wall image horizontally. The 271 linedef
does not flip the wall image, and it is intended to make it easier to take
existing non-flipped wall textures and transfer them to skies.
Sky textures which are different must be separated by non-sky textures, or
else the results are undefined.