(Dorji Wangchuk’s personal blog for pure speculations and reflections)
Your 2nd example is such impressive poetry, with the strong parallelism between the two lines. In the Dag yig gsar bsgrigs, it makes a distinction in meaning whether the tshad is used after a verb in present form or one in the past. I think it can work in both cases if you just translate "However much [there is or was]." And sometimes "No matter how much [there is or was]" which has a different ring to it.
Dear D, I would also think that in theory, it would work with all three tenses. With imperative, it would not. “Whatever I did/do/will do” .... D.