This idea is about introducing technology level and use it with multipliers. What about I said? There's technology called nuclear fusion, which can be researched many times. Imagine, player can research replaceable parts many times(for example three times) to decrease production cost of some units. Another think is nuclear fusion - there's should be effect called "add victory points" or something like that.
What you should do? Add multiplier field to technology information and maximum level of this multiplier (to technology level too). Moders could next use multiplier field in effect to change for example attack or production cost of unit. In player perspective, player simple select researched technology again and wait N turns to research next level.
Technology level
Re: Technology level
This could help some civilization game player, which loves creating custom units.