Puzzletome Crossword Puzzles

September 2013 Monthly Crossword
Over by Stozz

EDITOR'S NOTE:
This month's puzzle is compiled by a guest setter: 'stozz'. He would very much welcome any feedback you can provide, so please do use the feedback part of the entry form (or post on the forum) even if you don't complete the puzzle.
Stretham
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Twelve answers must be modified in one of two ways before entry into the grid. In six of these answers, the modification applies to one of the letters, increasing the word length each time. In the other six, the modification applies to a word within the answer, decreasing the word length each time. All modifications follow the same theme. In all twelve clues, the wordplay refers to the modified word.

A related four-letter word appears three times in the grid and should be submitted along with the grid.
Grid
Across
1Repetitive music on Taoist broadcast (8)
5 Stomach consumption of tips of aloe leaves and chili powder (6)
10 Get company backing team sport (5)
11 Flowery smell bishop found in filler (9)
12 Outrageous lie stated to believer (9)
13So upset about royal letter (5)
14 Queen is withholding honour for Cinders (6)
15 Divine right lost by bank starting to nose around is put back (7)
18 Manager of company having concerns initially of computer file back-up (7)
21 Inverted 90s band might produce roar (6)
24 Tragic flaw, hiding ugly head (5)
26 Odds on to receive nothing on account of bird (9)
27Old cross-beam supporting entrance to defended city (9)
28 More timid with head sunk, accommodating managers (5)
29 Man, for example, losing head over English former colony (6, 2 words)
30 Limits crushed ice going on top of rum sling (8)
Down
1 Playwright that hurt me, led astray (6, 2 words)
2 Divert junk e-mail after little while (9)
3 Janet arranges covered-up report (7)
4 Unfortunate beast, one circling black cats (7)
6Tiny amount included in some composition (7)
7 Football team losing final game - to do with the weather? (5)
8 21 tubes? (8)
9 I walk back to front, covering this distance? (6)
16 Keane finally dropped by former record company after 99 hits performed by this person (9)
17 Politicians sent to have a sort-out, misplacing model (8)
19 Kingfisher beer unfinished in hotel lobby finally consumed by Conservative (7)
20Duty of coppers to end racism (6)
21 Yorkshireman first to scribble American song (7, 2 words)
22 Yours truly books short break to compound (7)
23 Catches cold, girl having kept quiet (6)
25 Fashion workshop (5)