I agree, they don't trade players acquired in FA or players they've extended in the first season of their deals. Think Theo Ratliff to Charlotte was the only such trade and he wasn't a significant piece, besides it was his wish iirc.
Looking at the expected playoff 9-man rotation ( LMA, Pau, Gay, Kawhi, Danny, Manu, Kyle, Parker, Mills ) one would think Pau's and Mills's spots would be the ones they might look to upgrade and it's highly unlikely not only due to their contracts having just been extended, but they're the player with most 3s this season and the player with the highest 3 point efficiency. It'd be hard to replace this with anyone realistically obtainable on a team that has only 2 other good 3 point shooters (of the 9 playoff rotation).
They might make a smaller trade for the future though, as they don't seem likely to be able to keep all players. Bertans or Forbes could go. Lauvergne too (Theo Ratliff scenario), to make place for one of the bought out players if there's someone they like.