This method was introduced to me by xheadshotmastax.
It may not be the most "proper" way of fixing SLC, but it worked wonders for me.
I always used
DotHalo for all of my meta-fixing needs, simple yet effective.
For this tut I added Containment's "gate mach" to Elongation.
After adding the new tag to your map using Entity, open your map in DotHalo,
scroll down through the tags and find the new tag that you injected, take note of the new tag's meta offset at the top of the tag window.

Highlight and copy the tag's meta offset, we will use this to overwrite one of our existing native tag's offset.
We want to find an unused tag to reference this to, for smaller non-vehicular maps I tend to try and find a garbage [bloc] tag from a vehicle.
For this I used the [bloc] tag-
objects/vehicles/warthog/garbage/tire/tire
Using the copied meta offset from your new tag, paste/overwrite the offset of your native tag.

after doing so, don't forget to click the "Save Changes" button in the tag window.
And that's pretty much it... now just use whatever method you wish to spawn your new object, for example:
if spawning your new mach through the [itmc], you would reference the tire_bloc instead of the actual mach.
In my experience I've found that this can fix many SLC issues when injecting new tags, although I've only tried this method to fix machs, blocs, and bipeds.
But... I would assume that this can also be used to make your "alternate" weapons spawn in a pistols-only gametype.
For example, you would have to sacrifice the pistol for your rocket-launcher, by copying the meta offset of your RL, then overwriting the offset of the magnum .
And I'm guessing, but by doing so this should cause the RL to spawn in place of the magnum regardless of the gametype.
When I first heard of this method I told myself, "This sounds waaaay to easy!" But it actually works quite well...
I've used this during the making of many "mach-mods" that I have built and
I also used this technique to fix the "Buggers" in my Night-Ops MP mod, they were breaking SLC...
I pasted the biped's offset over a garbage bloc, then spawned the bloc through the char tag.
and if SLC really isn't an issue.. troymac1ure has the easiest fix.
