I have a red-eye LAS-ORD-MIA-TPA. I want to keep the routing for the extra few miles .

Let's say I take the LAS-ORD red-eye, get into ORD early morning but I really don't want to catch the following flights. I want to do the same combo but in the afternoon (need few hours in ORD). Assuming that for whatever reason the later ORD-MIA is full and I can't get on it, there are couple of more options left, fly through DFW or a direct ORD-TPA in the evening. Would that still be considered a normal standby as I'm trying to get to my final destination or would I have to pay a change fee for changing the routing?

And if you need to ask why I didn't book the exact flights that I wanted? because it changed the fare by almost double as it would be a stopover in ORD. (~8 hours). And, yes, I do realize I'm taking a chance, so no preaching. Thanks!