First, Hey welcome. Second, figured since I have made some mods in '98 I might have some helpful info.
While taking the wonderful expanded teams mods for '93, '94 and '95 into consideration, it theoretically *could* be possible to add another team to '98, it's easier said than done. I know there was a '97 based mod that tried to add the All-Star teams to the playoff format, but using them was a bit glitchy.
That said, including the All-Star/National Teams, you would have 31 total teams to work with already in the game, [yes 33 if you count the EA and THQ teams, but they just end up taking the place of the East/West teams] just that the last five would not be included in season or playoff mode. The other thing that you may have noted is that on the team selection screens, the team names are entirely sprite based, meaning that in addition to changing the text in NOSE, you would also need to edit the team name sprites along with the logos in Tile Molester. The unfortunate side effect of that is that some of the teams [like Team USA] have a limited number of sprites to work with so fitting the new names in there sometimes takes some creative hex editing as well.
Not sure if international hockey is your thing, but here's a thread with a pair of mods I made using '98 if it helps in dissecting the game. Also have some notes, not sure how easy it is to follow [I got rather lazy in making them], but I can lend some of those as well. https://forum.nhl94.com/index.php?/topic/20403-the-world-championships-series/