There is a superfluous word in each clue
Crossers won't help since the answer has to be doctored before entry
11a Athletic mother and devout woman believe in West Ham (10, 3 words)
13a Plant increased setback introducing rule in support (8, 2 words)
34d Sailor finally got a new sailing boat aground (6) "aground" is the extra here
For 21a An excellent specimen alphabet initially rejected by new Tatler (7) I think rattler is the answer and alphabet is extra, but how do I use "alphabet" to change the word... does it mean put the letters of rattler in alphabetical order or am i way offtrack here?