It is really easy to replace individual grommets. You only have to modify the grommet if it's too wide and won't go into the hole or if it's where you'd tie off and it's going to be too narrow to pass your tie-off end through. These individual grommets can get pulled into the hole or can wear down and expose frame so make sure to inspect all of them before stringing. Also, be careful when cutting out/removing string because the grommets can fall out and if you have a dark colored floor they are hard to find (unless you are barefoot, then you will somehow end up stepping on it. Murhpy's Law.)
Not sure what you are talking about the 'full effect'. If you are talking about how it plays (compared to say the single stripe POG w a grommet strip), the grommets have no effect on the feel. I'd think there's more variability in how it'll play due to the fact that you're playing with a racket that's over 30 years old that has been strung a hundred times and who knows where/how it's been stored or what abuse it's been through.