Changing housing bonus of TC's using triggers

Hi, I’m trying to test out a new civ and before I go directly into modding the game files I’d like to just setup a map and use triggers to get a good idea of how the balance would work out in a game.

One of the civ’s bonuses is dark age TC’s give 10 pop space, feudal 15, castle 20, and imp 25.

I’ve had some difficulty getting this to work using triggers and was wondering how the best way to do this would go since the single cause and effect nature of the triggers makes even slightly more complex functionality difficult to implement.

My current idea is by using variables and the modify resource by variable effect on population headroom.

The ideal way to do this would be if the player resource “current age” was simply 1,2,3,4 and I could put that into a variable, or call it using a script to do a simple formula…

#ofTC x currentAge x bonusAmount = bonu pop space…

trigger effect - modify resource by variable:
population headroom ADD bonus pop space

simple, but I dont know if it’s that easy…
so another way…

var bonus_amount = 5
var #ofTC
var totalPopBonus

if player has 1 tc,
set #ofTC to 1

if player has 2 tc,
set #ofTC to 2

etc

any ideas to avoid this longer way of doing it?