If you mean an upgrade like from a building, then do a trigger that checks for that upgrade and then sets a variable to the level of that upgrade, or just give each upgrade a numerical value.
Then when you spawn a unit you just have a trigger that adds certain abilities each time it's spawned and sets them to the variable number of the upgrade.
Or if it's a hero ability, just set a variable that is at 0, and each time a hero learns the ability, increase it by 1, or just check for the level of the ability at the time of summoning.
Something like
Event:
Unit starts casting an ability
Condition:
Ability equal to <summon unit>
Actions:
Set variable X to level of ability of <unit>
Unit> create summon unit at position of spell being cast or something, or position of triggering unit
Unit> Add ability A, B, C
Iunno.. something along those line, sorry in a hurry, otherwise I'd elaborate.
Edit:
Re-read initial post. You have to use Jass or Triggers for this type of thing, there is no way to do this sort of thing ingame without them. You can try all you like... but it won't work. I'm sorry but that's just how it is.