Combining REPLACE with SUM in one cell

[DiceCoDude]

I'm trying what I suspect is far easier than I'm making it.
I'm attempting to decrement the following cell by 4:
interface g1/0/5
the new text will be:
interface g1/0/1
I've tried a few ways with only slight success but I think this one is on the right track:
=REPLACE(A2, 16, 1, "?" ) - The question mark shows where I'm lost. I want to replace position 16 ("5" in this case) with the sum of position 16 - 4. Then I can drag the formula down the rest of my spreadsheet. This is a network switch configuration so I have to repeat this replace formula 240 times for each data closet, so... 48,000 times? I'm trying to find a way to save many hours of tedious work. MUCH appreciated.

 

[Fluff]

Hi & welcome to MrExcel.
Maybe

=REPLACE(A2,16,1,MID(A2,16,1)-4)

 

[JEC]

Is the last number is always one character?

 

[DiceCoDude]

Is the last number is always one character?

OH... good observation.. No. They will max out at "48" but no more than 2 characters.

 

[Fluff]

In that case how about

=REPLACE(A2,16,2,MID(A2,16,2)-4)

 

[DiceCoDude]

Hi & welcome to MrExcel.
Maybe

=REPLACE(A2,16,1,MID(A2,16,1)-4)

That is absolutely beautiful! Thank you. But to JECs point, I failed to mention that it'll grow to 2 characters. This formula works, but as expected when it grows you get this on gi1/0/10 "interface g1/0/-30". My fault!

 

[Fluff]

See post#5, we posted about the same time.

 

[DiceCoDude]

=REPLACE(A2,16,2,MID(A2,16,2)-4)

AND that is Perfect! Amazing. Thank you so much

 

[Fluff]

Glad we could help & thanks for the feedback.