With your " t1.client_code" I have to assume that you are using this where in Proc SQL. SQL in general is very verbose. So the may not be a way around this.
There is chance, slim and be extremely careful with this, if all of the values of interest are sequential that you could use
where t1.client_code between 'LBG001' and 'LBG003'
This will not yield expected results if the length of the values changes due to the way character values are compared:
data example;
input code $;
datalines;
LBG001
LBG002
LBG003
LBG004
LBG007
LBG00222
LBG000
LBG00
LB
;
proc sql;
create table want as
select *
from example
where code between 'LBG001' and 'LBG003'
;
quit;
Because the values of the between range have 6 characters the longer LBG00222 stops comparing at the first 2 and is "between" the range limits even though the second 2 would make a person think it doesn't fit. It may be possible to provide other restrictions in the Where, such as "and length(code)=6" but the particulars of each set will make this a potential exercise in making headaches.