Help Improve My Update Stored Procedure

need help improve my update PROCEDURE
i have this update PROCEDURE and it work ok but it is problematic
because i have to add all the time a new category 101,102,103,104,105,106 ........................
all the time i have to to rewrite the stored procedure and add new category

so my question is how to improve my update PROCEDURE
like for example create a table index

row_fld fld_index fld_text
---------------------------------------------------
1 101 a
2 101 b
3 101 c

1 102 e
2 102 f
3 102 g

1 103 h
2 103 i
3 103 j

--------------------------------------------------
so at the end i can add to the new table_index new category all the time
or update existing category



Code Snippet
ALTER PROCEDURE [dbo].[hofes_pro_stp2]
AS
BEGIN

update [dbo].[tb_pivot_big]
set fld1 = case v.fld1 when '101' then 'a' when '102' then 'e' when '103' then 'h' when '104' then 'k' end
, f1 = case v.fld1 when '101' then 'b' when '102' then 'f' when '103' then 'i' when '104' then 'l' end
, f11 = case v.fld1 when '101' then 'c' when '102' then 'g' when '103' then 'j' when '104' then 'm' end
, fld2 = case v.fld2 when '101' then 'a' when '102' then 'e' when '103' then 'h' when '104' then 'k' end
, f2 = case v.fld2 when '101' then 'b' when '102' then 'f' when '103' then 'i' when '104' then 'l' end
, f22 = case v.fld2 when '101' then 'c' when '102' then 'g' when '103' then 'j' when '104' then 'm' end
, fld3 = case v.fld3 when '101' then 'a' when '102' then 'e' when '103' then 'h' when '104' then 'k' end
, f3 = case v.fld3 when '101' then 'b' when '102' then 'f' when '103' then 'i' when '104' then 'l' end
, f33 = case v.fld3 when '101' then 'c' when '102' then 'g' when '103' then 'j' when '104' then 'm' end
, fld4 = case v.fld4 when '101' then 'a' when '102' then 'e' when '103' then 'h' when '104' then 'k' end
, f4 = case v.fld4 when '101' then 'b' when '102' then 'f' when '103' then 'i' when '104' then 'l' end
, f44 = case v.fld4 when '101' then 'c' when '102' then 'g' when '103' then 'j' when '104' then 'm' end
,

from [dbo].[tb_pivot_big] t
inner join (select *
from [dbo].[tb_pivot_big]
where val_orginal = 1) v
on t.empID = v.empID
where t.val_orginal = 2




tnx for the help