SQL Server 2014

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create table test 
(
  id int identity(1,1) primary key,
  col nvarchar(42)
);
insert into test (col) values
(N'HELLO 0123'),
(N'01234π56789'),
(N'abcdefghijklm>nopqrstuvwxyz'),
(N'ABCDEFGHIJKLM✓NOPQRSTUVWXYZ');
4 rows affected

--
-- Temporary tally table with numbers
-- Will be used to unfold that characters
--
if object_id('tempdb..#nums') is not null
  drop table #nums;
    
create table #nums (n int primary key);

with rcte as
(
 select 1 n, max(len(col)) max_n
 from test
 union all 
 select n+1, max_n
 from rcte 
 where n <= max_n
)
insert #nums (n)
select n 
from rcte
option (maxrecursion 4000);
28 rows affected

select t.*, a.scramble
from test t
outer apply
(
  select q.x.value('.','NVARCHAR(MAX)') as scramble
  from
  (
    select
     case 
     when substring(col,n,1) between N'0' and N'9'
     then substring(
      N'5678901234',charindex(substring(col,n,1),
      N'0123456789'),1)
     when unicode(substring(col,n,1)) between unicode(N'a') and unicode(N'z')
     then substring(
      N'nomrqputswvyzxiacbedghfjlk',charindex(substring(col,n,1),
      N'abcdefghijklmnopqrstuvwxyz'),1)
     when unicode(substring(col,n,1)) between unicode(N'A') and unicode(N'Z')
     then substring(
      N'NOMRQPUTSWVYZXIACBEDGHFJLK',charindex(substring(col,n,1),
      N'ABCDEFGHIJKLMNOPQRSTUVWXYZ'),1)
     else substring(col,n,1)
     end [text()]
    from #nums
    where n between 1 and len(col)
    order by n
    for xml path (''), type
  ) q(x)
  where q.x is not null
) a;


id
col
scramble


1
HELLO 0123
TQYYI 5678

2
01234π56789
56789π01234

3
abcdefghijklm>nopqrstuvwxyz
nomrqputswvyz>xiacbedghfjlk

4
ABCDEFGHIJKLM✓NOPQRSTUVWXYZ
NOMRQPUTSWVYZ✓XIACBEDGHFJLK

id	col	scramble
1	HELLO 0123	TQYYI 5678
2	01234π56789	56789π01234
3	abcdefghijklm>nopqrstuvwxyz	nomrqputswvyz>xiacbedghfjlk
4	ABCDEFGHIJKLM✓NOPQRSTUVWXYZ	NOMRQPUTSWVYZ✓XIACBEDGHFJLK