[Playbahnosh]

Okay, using _r.u.s.s.' idea, I created another pseudo-code, which replaces the timecodes instead of the subtitles themselves. Here:

OPEN file
X=0
IF search string "-->" returns result
   THEN:
       move pointer to location
       record line to variable T1
       delete line
       insert "00:00:00,000 --> 00:00:00,001"
       go down one line
   ELSE:
      msg: "Wrong file"
      END PROGRAM
END IF
REPEAT UNTIL X=1
   IF search string "-->" returns result
      THEN:
         move pointer to location
         record line to variable T2
         delete line
         insert line from variable T1
         move down one line
            IF search string "-->" returns result
               THEN:
                  move pointer to location
                  record line to variable T1
                  delete line
                  insert line from variable T2
                  move down one line
               ELSE:
                  X=1
            END IF
      ELSE:
         X=1
   END IF
END
SAVE file
CLOSE file
msg: "finished"
END PROGRAM

This is inarguably an easier method, and should be a cakewalk to put together, now.

Because the, fist line's timecode will be used as the second and the second's as the third...etc, I inserted a dummy timecode to the first line. By later deleting that line in-program, the indexing problem will be solved too.

A little help here?