While I can't be sure of your exact context, the things you've listed seem entirely reasonable activities for the role of "editor" (in a general case). Whether or not it's appropriate for the role of "reviewer" depends on what powers a reviewer has in your organisation. (Keeping this in mind, I'll answer in terms of how I see the role of "editor", since it sounds like that's what your reviewers are actually doing).
An editor may make anything from major structural and/or content changes down to fixing typos and grammar. Usually I would expect these to be in the form of suggestions, rather than outright changes that you (as the original author) have no control over. Is it the changes themselves that are the problem, or perhaps the way those changes are made that is annoying you?
Ideally an editor is going to maintain both the style and intent of the original author, assuming these are appropriate for the target audience. 873
In fiction you probably wouldn't want an editor changing your "style" (because the style is often part of the art), but in technical writing you want the style to be clear, concise and standardised (basically, to not get in the way of the reader's understanding).
If changing from passive to active voice removes words and makes something clearer, that can only be a good thing. Changing word tense would be reasonable to ensure the consistency of tense throughout the document. If an editor changes a word's tense and it is then inconsistent with the rest of the document, I would feel entitled to ignore/revert that change altogether.
If you think the editor's suggestions make things worse, you could either ignore the suggestion, go back to the editor to plead your case (negotiate), or accept it (if the editor is the "boss" and won't negoatiate anyway).
At the end of the day, if something is published with your name on it, you need to be happy with the finished product. If your editors aren't helping make things better, it may indicate problems beyond the technical changes they're making, but higher-level problems such as agreeing on who the target audience is, or whether they're competent editors in the first place.
As a final note, this may be an opportunity for you to develop a style guide for technical documentation in your organisation (if you don't have one). As long as you get everyone to agree to it, you can point at it for any "edits" you don't like. ;) 873