Special_replace2 ain't so hard:

DECLARE @MyString VARCHAR(100) = 'aaabbcdefgh'

;WITH Replacements (n,a,b) AS (

SELECT 1, 'aaa|bb|c|d|e|f|g|h','11|2|3|4444|5|6|7|8'),

Transform (ItemNumber, a, b) AS (

SELECT ItemNumber, MAX(a), MAX(b)

FROM (

SELECT n, ItemNumber, a=a.Item, b=NULL

FROM Replacements

CROSS APPLY DelimitedSplit8K(a, '|') a

UNION ALL

SELECT n, ItemNumber, NULL, Item

FROM Replacements

CROSS APPLY DelimitedSplit8K(b, '|')) a

GROUP BY n, ItemNumber),

rCTEReplace (n, s, r) AS (

SELECT n=1, MyString, REPLACE(MyString, a, b)

FROM (SELECT @MyString) a(MyString)

JOIN Transform ON ItemNumber = 1

UNION ALL

SELECT n+1, s, REPLACE(r, a, b)

FROM rCTEReplace

JOIN Transform ON ItemNumber = n+1

)

SELECT *

FROM rCTEReplace

WHERE n = (SELECT COUNT(*) FROM Transform)

Ain't gonna win no performance contests though! 😛