I booked a two night stay, but something comes up, so I would have to arrive a day later than the reservation's arrival date (so stay for 1 night instead of the originally planned 2 nights). It's too late to cancel/modify cuz deadline has passed and it's a prepaid rate. So i am ready to give up the first night rate since it's a cheap rate.

So would it be possible to use mobile check-in to check in for the first night, and arrive after the first night without having to go to check-in counter when i arrive?

I am not sure if the hotel has mobile key, so if mobile key is not available at the property, would it be possible to call and check in and pick up the key the next day?