I wish I had discovered this thread earlier. I disassembled my grill too and thought it was easy,
but reassembling the thing was an absolute nightmare.
Took me several hours to put it back together (and I had to disassemble it again halfway through
because while driving I suddenly heard one of the clips move around, which meant it was dislodged!)
I found a way to make reassembly easier:
1. Move the grill into place and make sure the angled plastic guides are inserted into their slots.
2. Now lower the grill into place. The nubs won't fit into their slots because of the angling.
3. _Without_ applying downward pressure onto the grill, use a flathead screwdriver to apply pressure to the nub to slightly nudge it back.
4. While pushing the nub back, slowly start applying downward pressure on the grill to slide the nub into the slot. It should not require a lot of force.
The key is to not use too much force. If you you apply downward pressure in step 3, it can cause the nub to be in contact with the clip, and as you push with the screwdriver, it will actually dislodge the clip. Also, you don't need to significantly move the nub back, so don't apply so much force that you break the thing. Using the screwdriver to push the nub replaces the effort needed to somehow warp/flex the entire grill into the right shape to insert the nubs.
I have small hands so I was able to manually retrieve most the dislodged clips without too much effort. But the one clip you absolutely don't want to dislodge is the center speaker clip. Turns out, it can actually fall _into_ the hole for that clip, and you have to remove the center speaker in order to retrieve the clip. Removing the center speaker requires unscrewing 3 torx screws, and one of them is so close to the windshield that the only approach I found that would work is to use a plier and grip a drill bit. Incredibly tedious and took a really long time.