Extra Effort solution
by Kegler

As indicated by 20A 32A, PUTTING IN A LITTLE OT, fifteen answers have OT added to form new words or phrases before entry.

Extra Effort solution grid

Across
1F(LAX)EN
6SP{OT}LIT (2 defs)
11L{OT}ION ("LYIN'" hom)
13SO(O)N
15ON + E
16NAG (hidden)
17BA(L)L{OT}S (SLAB rev)
18TEPEE ("T.P." hom)
19TOY (hidden)
20PUTTING IN
21ER{OT}IC (RICE anag)
23NOH (HON rev)
24S(PA)R
27S.A. + USAGES
28TINe
29EPEE (hidden)
30HURT (2 defs)
32A LITTLE OT
35T,{OT}E + D
36C + ENTRIC (CRETIN anag)
37MERINO (hidden)
39CAME + L{OT}
40STINGY (2 defs, pun)
41K + EY(N){OT}ES
42ROSE (2 defs)
Down
1FO{OT}REST (SOFTER anag)
2LINEAR (I LEARN anag)
3ALE + PP + O
4ETA (hidden)
5NIGHTCAP (PATCHING anag)
6SO + BRIQUET
7OSLO (hidden)
8TOL + LING (LOT rev)
9LO{OT}
10INT{OT}O (TONI anag)
12N(ANN)Y
14PSY + CH{OT}IC (SPY anag)
16NEUTRAL (RENAULT anag)
22HeAVEN{OT}S
23NE(U)T + RON
25PIN{OT} (NIP rev)
26A + NA(TOM)Y
27S(E)IDEL (DELIS anag)
30cH{OT}AIR
31STUC + K (CUTS rev)
33TAR{OT} (RAT rev)
34SIN(G)S
36CITE ("SIGHT" hom)
37M(E)N
38BYE ("BUY" hom)