There will be minor balance changes.
Note that I'm working from the Earthdawn revised edition, because I don't have my first edition hardcover handy; I think the initiative rules are similar enough to be identical for the purposes of this question, but it's been a while since I played first edition.
You're going to change something that doesn't have a huge impact on the system as a whole; when I played Earthdawn it was something that my group just sort of did automatically and I didn't have the guts to fight them, but it does have some minor changes to the balance, and it mostly revolves around certain combat conditions.
The purpose of the declaration of actions is to encourage people to decide on a course of action with uncertain events, and it does impact some tactical decisions. If you had three enemies, one of whom can deal and take a lot of damage, and two of whom can't, you'll see changes combatant behavior, because previously people who decided to gang up on a big guy would take a slight penalty if he goes down during that combat turn and they go to deal with one of the little enemies.
In my experience, the results of changing initiative were insignificant in the long run, though I didn't ever do a whole lot of Earthdawn; most of the time the results weren't meaningfully altered. Of course, the system in the revised edition also functions as an indecision tax, which might be helpful for maintaining discipline in certain groups, but even with my somewhat squirrely group there wasn't any real need for it, since players tended to commit to their course of action until something really dramatic (like an ally/enemy dying) happened, and that usually shifted the balance enough that the penalty for changing actions didn't change players' minds.