I thought I would go ahead and chime in.
LINE-X has a patented process (which won a SEMA award in 2008) called ReNew. ReNew can be used on ANY brand of spray-on bedliner. The process includes a new textured layer and the use of LINE-X Xtra, so the bedliner will not fade or lose it's gloss.
Prior to ReNew, LINE-X dealers cleaned the bedliner and then applied a special primer prior to the application of the new bedliner product. This also works, but using the primer was not always convenient (for reasons I won't go into, it's a long story).
I can tell you that just cleaning the bedliner and then spraying a new coat will NOT work, no matter what the brand. It will eventually fail by delamination due to poor or no adhesion of the layers.
A local body shop took a truck that needed just one bed side sprayed to a Toff dealer in my area (who is now closed). The rest of the truck bed had LINE-X. The Toff dealer spray the side as well as the rest of the bed so that the entire bed looked the same. Well, the respray failed. The body shop then brought it to us. We had to strip the entire bedliner out and start all over again. Here's some pics of the delamination:
http://img.photobucket.com/albums/v4...TRiggpeel1.jpg
http://img.photobucket.com/albums/v4...TRiggpeel3.jpg
Bubble:
http://img.photobucket.com/albums/v4...nds/TRigg1.jpg