I would like to add the string "1212" (no quotes)
to some part numbers.

Essentially, I have two versions of part numbers
to modify:
xxxxxxx(space)(space)xxxxxxxxxx
or
xxxxxxxxxx(space)xxxxx(space)(space)xxxxxxx

The length of the xxxxxx strings varies and represents
alphanumeric characters that must remain unchanged.

The end result of the modification should be as
follows:
xxxxxxx1212(space)(space)xxxxxxxxxx
or
xxxxxxxxxx1212(space)xxxxx(space)(space)xxxxxxx

Would somebody please suggest how to do it? This is
beyond my knowledge of Excel.

Thanks in advance.
----
Tiziano