Forgetful
by Kegler

Ten answers have to be given special treatment before entry into the grid, as indicated by the unclued center entry.
When read in clue order, the first letters of the clues for the ten affected entries describe what the solver is entering.

Across 1 Rubbed mother's wise friend's back 8 Lie next to reflecting instrument 12 Remain undecided after dad returns with supplement 14 Stooped, as intended, losing bit of stature 15 Agile agent obtains core of secrets 17 Drink is a place to start, reportedly 18 Weird home page describing musician's latest amplifier 19 Predictable trace of lisp in scornful expression 20 Call a normal stocking “plain” 21 Bring in rotten pear 24 Hysterically odd wit for survivor of a shipwreck? 25 See instructions 29 Show's finale rings with cries of excitement 31 Northern primate’s back of the neck 32 Irate man of the cloth collaring woman of the evening? 34 Make an impression with boat after end of week 35 Author Anita set off, most relaxed 38 No reason, at first, for conjunction 40 Lovely festival 41 Stooge capturing market for white wine 42 Tenor crooner with broken ankle initially tightens wrapping 43 Eager newspaperman, carrying on, originally shunned 44 Alienate foreign sergeant

Down 1 Sam returns top of totem pole 2 Papa upset by John while returning horse 3 Pair of speakers interpret range 4 Provider of funds for one hair product 5 Dame shredded cheese 6 Guard in back gave instructions to stop 7 South China Sea island, distressed about Inga, starting to panic 9 Releases pair of ungulates (deer) 10 Conk outlaw carrying rifle, finally 11 Heard commercials for tool 13 Goal I'd bandied about in conversation 16 Silly expression about her unoccupied boat 17 Prudence rumpled fine T-shirts 19 Essayist's breakfast food 22 Connecting with lawyer, briefly, hurting 23 Leaders of parish's stellar youth choir help cause emotional excitement 26 Clean off empty limousine's engine housing 27 Agitated Tobin is accommodated by board directly 28 Mate, drunk, gulps drop of port 29 Cetacean swallowing sole, head to tail, indiscriminately 30 “Variety” reader ultimately in disgrace 33 Shrink beginning to call one who hasn't paid 35 Monk essentially follows medical group 36 Embarrassingly boo Ovid's “Shaped Like an Egg” 37 Unusual site for stalemates 39 Press throw rug and drape, eventually

Solution