Regarding Musketman as UU. Look at the French and Ethiopians. Make sure the Scandinavian one isn't very much better or worse than these.
Orormo Warrior has:
1 First Strike
Immune to First Strikes
Starts with Drill I & II
Musketeer has
2 Movement
Perhaps find something that isn't very much alike.
What about a strength bonus or discount instead?
Still a good iniative
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After looking at Wikipedia, the Caroleans are described as tougher and never retreating.
Since Musketmen are so short-lived, why not give them strength 12? Still they will be
subsituted for Riflemen, but allows you not to rush for Rifling
(It's a bit contrary though, since they "lived" only for about 20 years")
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Another thought:
Give them "Leadership" (+100%Xp from Combat)
This would have to be removed by upgrading, or way too powerful
This promotion is normally only avaiable through a Great General,
but it would be flavour: Fight as much as possible, and never upgrade
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Norwegian UU:
What about a Berserker which gave extra pillaging gold? (+20% for instance)
This would be a very original trait. Scripting needed of course.
Should keep Amphibious, but for not making it stronger than the normal Berserker,
make some penalty.