“Can owner in common alter their half of electrical panel without consent of other party? If the electrical system is condemned can it then be altered for necessary repairs to bring up to code?”
I’m taking from your question that you are a co-owner of a property (either a tenant in common, a joint tenant, or some similar type of ownership), and that there’s a disagreement regarding whether some maintenance (electrical panel work) ought to be or needs to be done.
So, as a general matter, co-owners each have the right to use the property, so long as they’re not “excluding” the other co-tenant. If one co-tenant expends money to preserve the property, that person is entitled to reimbursement (at sale, if not immediately). The question, then, is whether the work you do is in fact preserving the property, and that’s a question of fact. If the city/county condemns the property, I’d say you have a good chance of winning that argument, but short of that it just depends on the particular facts.
So short answer: Yes, you can do maintenance and repairs such as upgrading the electrical (so long as what you’re doing isn’t wasteful and isn’t excluding your co-tenants from the property). However, whether you’ll get repaid for that work depends.
By the way, if you take the time to have a co-ownership agreement prepared before you enter into a co-tenancy, a lot of these fuzzy questions can be resolved in advance. It’s definitely an ounce of prevention that can be worth more than a pound of cure.