Transformation solution
by Kegler

As suggested by the central entry, A CHANGE OF STATE, twenty-five answers have one state abbreviation replaced by another  
to form a new word before entry. The state changes are shown below in brackets and highlighted in the grid by the shaded squares.

Transformation solution grid

Across
1SEALION (IS ALONE anag) {AL->CT}
6SP + ANGLE {PA->HI}
11LOWSLUNG (GULLS NOW anag)
12DR(A)Y
13mARGOT {AR->IN}
14STA(P)LE
16ORT (ROT anag)
17LENS (2 defs)
18AS(I)A {IA->KS}
20NLER (last letters)
21E(MOT)ED (rev) {MO->LA}
22WAiTER {WA->ME}
24ETA (TEA anag)
28F(I)RED
30CRE(P)ES
31P(I + ON + I)C
32A CHANGE OF STATE
34PH + O + TOS (SOT rev)
36P + ASSES {PA->MO}
40LASER (EARL'S anag) {LA->WI}
42ERA (2 defs)
43ENTER (hidden)
45B,R + EWER
47CAWS ("CAUSE" hom) {CA->NE}
50ELBA (ABLE rev)
52INTO (hidden) {IN->AL}
53DAY (2 defs)
54[T/m]EDIUM
55STALK (2 defs) {AL->OR}
56VETO (VOTE anag)
57STRATEG + Y (TARGETS anag)
58AR(RAN)GE (RAGE anag) {AR->DE}
59L(E)AD + SON
Down
1SANDED (hidden) {ND->IL}
2MA(GNA)TE (NAG anag) {MA->CO}
3T + WOS + TEP (rev)
4IST(L)E (TIES anag)
5NaILS {IL->UT}
6SN + ORE {OR->AK}
7MOLE (2 defs) {MO->ID}
8COO(L)ER {CO->GA}
9LYRE ("LIAR" hom)
10ENTR'ACTE (AT CENTER anag) {CT->NC}
14S(A)D
15EN(ROO)T (NET anag)
19STE[P/m]
22WAXERS (RAW SEX anag) {WA->MI}
23EDISON (IS DONE anag)
25TILTER (LITTER anag) {IL->RI}
26RIC(H)ER {RI->AR}
27RENOWN (hidden)
29ROO + FER (REF rev)
32AP(PEAR)E + D {AR->ND}
33A + T + TEST
35SITE ("SIGHT" hom)
37S(W)EATED
38SAW + LOGS
39SAILER (ISRAEL anag) {IL->WY}
41BRA + ZEN {AZ->OK}
44ELITE (hidden)
45B + AM
46R + ASTA
48E(A)VE
49PE + ON
51B + URL