At minimum, the Grim Forrest Advanced Quest should be just like the Sintranos Advanced Quest where you can rerun already completed stages and have it count.

Will point that out to the CMs. 

same, idk if i can manage to defeat one of the many challenges I have in front of me, but it doesn't look likely

Also,

I want to make use of one of the champions in my grim deck, but i cannot because it is in my grim deck.

I would like to be able to remove a champion from the deck, leaving it minus one, or two, till the end of the current run.  Or, also be able to complete the run early, just ending it, to be able to do whatever I want with those champions instead of them being locked.  In other words, eating one or two of em.  (sometimes i don't like one and don't want to keep it, even if everybody else does.  In the case of the Alien, I sold my 2 and 3 star awakening items before realizing I need them to use the 4 and 5 star ones, so I am about to eat my Alien to upgrade a 5 star champion.  I have a 6 star fortress goon awakening soul but I need to advance him to 6 stars.  Anyway, I will use some greens.  But the Alien is going bye bye.  Also eating the Alice.  It's ok, but too cute for me, and I don't think it fits in Sacred Order at all.  And I don't much like the free champs and every other person having them, my 2 cents.  So I eat them, usually.  I can't think of one I still have.)

So, two options I would like, remove a champion from a deck.  End the grim forest early for the current cycle.

And put a reroll button on the quest like there is for the other advanced quest, at least out of grim forest.

As long as the champion you are wanting to remove isn't in an active draw on a stage that you haven't beat you can use the Squad Reshuffle to remove it from your deck. You can remove up to 5 champions per difficulty. 

i

I believe the devs are also looking at the issues with swapping champs in and out of the deck.