You can have a go - not something I would do to be honest, far too specific for a single solution. OK, you might have hundreds of these drawings to do, but to write, check, verify, try to break a code before you finally use it usually is more time consuming than just doing it for a few drawings (of course, other times I do that just because I can)
This will select all the text that is a height of 2 (according to your drawing) (refer to Lee Macs website for ssget references - his is probably the easiest for me to understand)
(setq MySS (ssget "X" '((0 . "TEXT")(40 . 2))))
This will loop through the selection set and update your text.
(setq acount 0)
(while (< acount (sslength MySS))
(setq MyEnt (ent get (ssname MySS acount)) )
;;Do Your text changes here, save as variable NewText
;;https://help.autodesk.com/view/OARX/2023/ENU/?guid=GUID-C7D27797-247E-49B9-937C-0D8C58F4C832
(setq MyEnt (subst (cons 1 NewText) (assoc 1 MyEnt) MyEnt )) ;;
(entmod MyEnt)
(setq acount (+ acount 1))
) ;; end while
and how you want to do the texts and any verification that each is a number is up to you - loads of options out there. The simplest would be a mix of the ascii and chr functions with a +1 which would increase by 1 the last digit and no error checking that the text is a number. There is a method out there to add all the ascii characters together so that +1 will do 10s,, 100's and so on if necessary (this method will work for letters if you ever get that case. versatility), or else you want to do a check that the text string is a number (this is all online somewhere), convert to a number then +1 (use ATOI for integers, ATOF if you might have decimal places)
Remember that NewText has to be a string, if you calculation gives you a number it wants to be (rtos Newtext) in the substitution line
You might want to add in start and end undo markers in case it all goes wrong sometime (this is online),
How long you spend making it nice depends how often you will use this, but the basics are above, and in the original thread you copied the code from (always good to give a link to there, there are other ideas in that thread if what you posted doesn't work for others following you)