Creating Effect question

When a GM create a custom Effect and set a duration is it possible to decrease/increase the Effect for every step of the duration?
Example: I want to create a Effect for a drug that decrease your END (endurance) by 5 for 5 days. But what the effect to slowly wear off by 1 point for every day and not go from 5 to 0 on day 5.

And also can I create a Effect that takes a variable as input when assigning it.
Take the the previous drug effect example. I want to have a Effect that decrease your END by X for X days. So when I drop the Effect on a player is ask me to input X as a number.

Originally asked about Traveller but think it applies to all rulesets because it more about the capability in FGU

Effects are unique to each ruleset. So its possible that one or more rulesets have this capability, but I know D&D 5E pretty well and its effect system does not support what you want.

Same with the second question, maybe there is a ruleset that supports, but in general, no. In part because the CT does not normally track days, but you also don't get promoted for a value when you apply an effect.

You also might find an extension in the Forge that does what you want, but you will have to know what ruleset you are interested in.