If there will be possiblity to start from multiple points of time with already unlocked researches and predefined base then Xcom files instantly become FMP 2.0.
It is like
Select starting chapter:
1) Begining of the X-com (Deafult start).
2) We know- they are coming (Promotion I or II, later by time)
....
N) Aliens invasion (familiar fighting with aliens, starts with invasion time).
It can be even synronized with arcs.
Is it technically possible?
You can modify the mod
Or move all your changes to a separate mod. Once you figure what needs to be changes, it's pretty straightforward. The biggest problem would be that XCF is still evolving. What made sense 2 months ago, may no longer work as desired.
This approach limits you to a single starting base and doesn't allow to get veterans or screen agents' abilities. I have not searched how are UFO missions in January 1997 implemented, but probably they just won't happen.
That said, you need to find and alter the following:
startingTime — in Ruleset/vars_XCOMFILES.rul
initialFunding — ditto
startingBase — in Ruleset/startingBase_XCOMFILES.rul — add new items to the store, facilities, vehicles to hangar, increase number of agents/workers/researchers; maybe add some yet-unresearchable trophies, e.g. Mind Probe for January 1998.
fundingBase in countries — in Ruleset/countries_XCOMFILES.rul — for each country.
To move the plot forward, you need to enable certain pieces of knowledge. I don't know how to do that — ask in other subforums. It's at least possible to give corresponding items in Ruleset/research_XCOMFILES.rul "cost: 0", "points: 0" and empty sections "dependencies" and "requiresBaseFunc". This way you should get a lot of research items at the end of 1st day — messy, but gets the job done.
What to enable is up to you. For example, if you set the date to March 1, 1997, you should do something like:
add to the base Biolab and Intelligence Center,
replace the car with 2 vans,
increase number of agents to 10, scientists to 15,
add to the store some Earth weapons,
add pieces of a captured UFO and some low-level alien weapons, if you assume the agents should have captured UFO(s) in January,
in research enable Promotion 1 (STR_MILESTONE_1_SUMMARY), biolab (STR_BIO_LABORATORY), intelligence center (STR_INTEL_LABORATORY), van (STR_VAN) and research items that lead to them (within reason):
- STR_MILESTONE_1
- STR_STRANGE_CREATURE_AUTOPSY
- STR_REAPER_AUTOPSY
- STR_REAPER
- STR_REAPER_TERRORIST
- STR_SECTOID_AUTOPSY
- STR_GIANT_RAT_TERRORIST
- STR_GIANT_RAT
- STR_GIANT_RAT_CORPSE
- STR_GIANT_BEETLE_TERRORIST
- STR_GIANT_BEETLE
- STR_GIANT_BEETLE_CORPSE
- STR_ZOMBIE_STERILE_CORPSE
- STR_ZOMBIE_STERILE
- STR_ZOMBIE_STERILE_TERRORIST
- STR_CULTIST_INTERROGATED
- STR_EXALT_INFILTRATOR
- STR_ZSRR_GANGER
- STR_BLACK_LOTUS_FOLLOWER
- STR_SUPPORTER_OF_DAGON
- STR_ADVANCED_MEDICINE
- STR_MEDICINE
- STR_BASIC_OPERATIONS
- STR_CHURCH_OF_DAGON
- STR_BLACK_LOTUS
- STR_ZSRR
- STR_EXALT
- STR_VAN
- STR_LOGISTICS
From my perspective... definitely not doing any support for this in the code.
How about enabling some research items at the start of the the campaign? Does the engine support that?