Try this:
For 1-100
UPDATE table
set new = 'A'
where id in
(
Select temp.Id from
(
Select id as Id from table limit 1,100
) as temp
)
For 101-200
UPDATE table
set new = 'B'
where id in
(
Select temp.Id from
(
Select id as Id from table limit 101,100
) as temp
)