verse 29 and those scriptures are talking about the Jews corrupting THEMSELVES, read verse 29 ... it says "corrupt YOURSELVES"
Not corrupt the scriptures. Big difference. The scripture is talking about how after Moses will die Gods people will "corrupt" themselves, meaning turn away from the true path and go back into Idol worship etc etc and basically, "forget his benefits" if you like.
This has nothing to do with corrupting the scriptures, its talking about the jews corrupting themselves. Verse 29 even says "corrupt yourselves". How clear can things get.