Coupling
by Kegler

In the 14 squares where the Across and Down entries conflict, both letters should be entered in the grid.
The unclued entry at 29 Across explains what you are doing. (Note: 29 Across does not apply to itself.)

Coupling grid

Across
1Most of our standard parts came in disguise (10)
9Pull sled without energy (3)
12Hawaiian greeting Al with wreath and laugh (5)
13Front of dilapidated cafe (4)
14Jump in lap, hugging uncle at last (4)
15Posers seldom resolved (6)
16Reportedly visit a body of water (3)
17Sit around university clubs, for example (4)
18Crew member to seize one group (7)
19Encouraging for swelling to start late (6)
21Western friend takes, for example, two pieces of Bolivian wood with holes in it (8)
25Cheer for catching small perch (5)
26Coming from Dublin, maybe, dropping husband's flower (4)
27Choose subset of Top Ten (3)
29See instructions
30Before every other learner ... (3)
31...misinterpreted test, let it stand (4)
32Crazy nut that is free (5)
33Run another strand through patched-up tire filled with hydrogen (8)
35Seizures of resorts supporting heartless scam (6)
37Fit last bit of assignment between “catch some rays” and “drink” (7)
38Poverty ultimately dashes desires (4)
40Course number leads to professor's alternate room (3)
42Horse around at take off (6)
43Church calendar's door slammed (4)
44Beginning to transport sheep in railcar (4)
45Miriam is erotically embracing Ebenezer, for one (5)
46Greek character's audible lament heard (3)
47TV rejected separating Italian poet's girls (10)
Down
1Taper line appearing in whipped cream (9)
2Icy one repulsed jester (5)
3Developed and imposed our way of doing things (5,8)
4Friend rented platform (6)
5Endure some of guerilla's tactics (4)
6Flyer races between terminals (3)
7Tackle finally catching the Atlanta runner (4)
8Trains golfer Ernie (3)
9Unfortunately, I spotted peril for one with a net? (13)
10Crumpled up final causing grief (7)
11Stomach return of harbor vessel (3)
19Macabre author describing, in time, ballet position (6)
20Earth eventually becoming spherical (6)
21Practices with Herb welcomed by you and me (6)
22General adjusted shirt and waist measurements (6)
23Cheese grater's back with Rose, perhaps (5)
24Ships bearing red flags (9)
28Awful rugs are the sources of some protests (7)
32One morning, wearing Dad's straw hat,... (6)
34...binge with wild peers (5)
36Returning wet umbrella, keeping quiet (4)
37Piece back in corner (4)
38Discussed evergreen tree with second person (3)
39Pop doesn't finish grass (3)
41A real British trader (3)

Solution