Update: see TayMcKenzieNZ's post on the forums for additional information and hints.
A forum post has been written detailing how to use modified scenarios on FiveM servers. The gist of the post is as follows:
However, what should work is registering a replacement scenario point manifest:
take sp_manifest.#mt from update:/%platform%/levels/gta5/ from 1604 if you use it! if you use the 2189 one on 1604 you'll crash with ERR_STR_PACK_2 as island scenarios don't exist!, (contents of, as XML) UPDATE: this file will break some stuff if used as XML verbatim and there's "hash_" in there. use CodeWalker's 'save' option to save an edited file as PSO instead.
specify it as data file:
file 'sp_manifest.ymt'
-- SCENARIO_POINTS_FILE may work, too
data_file 'SCENARIO_POINTS_OVERRIDE_FILE' 'sp_manifest.ymt'
edit it:
<Item type="CScenarioPointRegionDef">
<Name>compcache:/test_ymt/countryside_ne</Name> <!-- apparently VFSRagePackfile doesn't support RSC registration, so we use `compcache` instead of `resources` here -->
<AABB>
<min x="577.9417" y="-2190.842" z="1.645161" />
<max x="2970.658" y="6642.504" z="355.7393" />
</AABB>
</Item>
make sure file 'countryside_ne.ymt' is in your resource's stream/ folder
yay!