Whilst getting acquainted with Solars, I happened upon this rather... patchwork method of simulating RunningLights (and other effects) as buyable / mountable. It's certainly not perfect. But for its limits, it still offers a bit more customization -and with some creativity, some interesting opportunities for all sorts of ship upgrades. Essentially it boils down to the equipment already being present in Shiparch.ini / good.ini package. *You are actually buying a HardPoint as a commodity / equipment, to "unlock" the item associated with that specific HP.
Here are the relevant ini sections:
ST_EQUIP.INI section
[Shieldgenerator]
nickname = Plight01r
hit_pts_scale = 1.25
hit_pts = 19000
HP_child = SpConnect <-stock shield entry is HPConnect which is why mine didn't show up at first
category = equipment
ids_name = 0 ;GENERATESTRRES("Mountable Red Light01")
ids_info = um, yeah, stuff here
DA_archetype = equipment\models\st\Plight01r.3db
mass = 10
volume = 0.0000
lootable = false
debris_type = debris_normal
hp_type = hp_freighter_shield_special_1
ST_GOOD.INI section
[Good]
nickname = Plight01r
equipment = Plight01r
category = equipment
price = 10000
item_icon = equipment\models\commodities\nn_icons\equipicon_weaponupgrade.3db
combinable = false
ids_name = 0; ("Mountable Red Light 01")
ids_info = 0 blah
shop_archetype = equipment\models\commodities\nn_icons\equipicon_weaponupgrade.3db
Of course, this method will require quite a few copied / renamed shields, but I suspect you already can imagine the lovely headaches ahead :p
SHIPARCH.INI
just set up a hp_freighter_shield_special_1 we'll use HpLight01 here
MARKET_MISC.INI
[BaseGood]
base = ST04_01_Base
MarketGood = Plight01r, 0, -1, 100, 100, 0, 1
GOODS.INI
addon = Plight01r, HpLight01 <-- your new hp, which you sadly had to make on every ship you wanted a light on 
addon = SlowXLargeRed, HpPlight01r <--- this is the HP you added via UTF edit to the shield.3db "model"
If you're wondering which shield model I'm referring to, go to \data\ships\liberty\LI_FIGHTER\ li_fighter_shield.3db
that only contains a hardpoint (which you need to set the position for to 0, 0, 0 and then add the unique light Hp as well)
rename the shield to same as hp for ease, and repeat.
The downside is for every light you want to be mountable, -with this method they must be declared / equipped and "built into" the model that way. So essentially the shield you buy with the light's name acts as a key to switch that already existing light on.
Addendum:This does have some other nifty applications as well though. Player Ship upgrades , for one: special thrusters or power plants, and built-in weapons, as well as whole ship sections (modular ships weee) -like perhaps macross fighters with the booster packs as an upgrade.
By the way, this still needs to be tested on a server before going into production. I've only tried it in OpenSP mode.