I'll copy and paste what my friend sent me!
"ALREDY KNOWN FACTS
You can't use the modded incline / bridge as the first one you place or you will lose the ability of placing more
you can talk to only one Lloid, so if you place 2 inclines/bridges you will be able to talk to only one of them
paying one incline/bridge and then placing another one will make you have to pay again for the first one
NEW FACT
If you will place a lot of inclines/bridges (10+) you will permanently loose the possibility to have Redd on your island
EXPLANATION
This happens because placing inclines / bridges will edit a building slot from 0 to 27.
how will that effect redd? well, when redd is not on your island his own slot becomes 0, and when he comes to your island it becomes 28.
changing the value from 0 to 27 will prevent him from spawning, because before spawning he will check for a 0 building located in a specific place.
so, can you just delete the bridge / incline and he will spawn again? NO, because he also checks for coordinates, and positioning the bridge/incline will change the coordinates of the building slot. so, be careful with that.. you will not be able to recover it."