Maybe my brain’s fritzing, but I can’t think of a single-letter change that will turn DUMB into any other word.
Numb and dump will both work.
Yup, brain fritz. 
Thanks.
Dumb -> Dump -> Damp -> Dame -> Dane -> Dank -> Dunk - > Duck -> Luck
GOOD -> WILL
GOOD --> WILL
good
fool
fowl
bowl
boll
bill
will
SOUL --> CAKE
Soul -> Soil ->Toil -> Tail -> Tall -> Tale ->Take ->Cake
SOFA -> SEAT
Soul
Saul
Sauk
Sank
Sane
Sate
Sake
Cake
Doh!
Sofa
Soft
Sort
Port
Pert
Peat
Seat
Soda > Beer
Soda - > Coda - > Code - > Core -> Bore - > Born - > Boon - > Boor - > Boer - > Beer
Whew.
EVIL -> STAR
evil
eval
aval
avar
atar
star
My fist one… did I screw up?
lane > road
Depends… are all those real words?
evil
eval
egal
agal
agar
atar
star
Slightly modified, as it said aval had an entry but it was an acronym.
lane > road
lane
land
lend
lead
read
road
dogs --> cats
dogs
cogs
cots
cats
(I think I had an easy one, what with all the pluralization…)
Love -> Nest
Love
Lose
Lost
Lest
Nest
I had an easy one too.
Love --> Bird
Love - lose - lost - lest - nest
PLAY --> GAME
See post #6. 
LOVE
lore
lord
lard
bard
BIRD
FOOL --> KING
FOOL
food
fond
find
kind
KING
BUSH --> GORE
Bush
Bosh
Bose
Bore
Gore
Drmatrix > Cajunman