One word in each clue must have its first letter changed to an H for the clue to work properly. Once the grid is filled, the two unclued entries are FRIENDS STAR / HOLDS A CABLE, which is a cryptic clue for CO(A)X. Changing the first letter of that answer to an H gives the solution, HOAX.
ACROSS
- 1 [heart] T + rUSh + KisS
- 4 [hack] gazpaCHO Periodically
- 6 [heave] E + JE(C)T
- 8 [hoops] ARE + N/A
- 10 [has] CHAISE (anagram)
- 16 [hopping] T + O + AD
- 17 [hollow] TerI + LE
- 21 [heard] ALLEGE (“a ledge” homonym)
- 22 [hoard] S(T)ORE
- 23 [Hades] vioLET HEather
- 24 [hit] RA(M)P
- 25 [hogs] O + INKS
DOWN
- 1 [half] T + W + ELF + THe
- 2 [hurt] SPECIAL (anagram)
- 3 [Hell] SAT + A + N
- 4 [home] uCLA’S Schedule
- 5 [Hornets] PI(NBA)LL
- 7 [hides] wretCHED DARjeeling
- 9 [housing] R(E + ST.)AGE
- 11 [hands] I + DEAL
- 13 [hen’s] R(O)OSTER
- 14 [Homer] TI(BETA)N
- 15 [high] R(E)EFER’S
- 19 [hiking] SLEEP (peels reversal)
- 20 [hi] C + hELLO