Firstly we're talking about one question, that has some downvotes and is not being flagged as spam or abusive, nor are we talking about a string of downvoted questions. There is not enough here to get an ip ban (afaik, as the algorithm is hidden in the sacred coffers of SE).
As for accounts, you can either create an account on site Y, linked to your current account on site X. Or you can start a new account on site Y that is separate. There are restrictions with IP addresses if a person is trolling the site, or has a post ban, to circumvent this, but as you have no account on site Y, there can be no ban. If you were to receive a post ban on site Y, there would be no option to create a second account to circumvent that ban.
The normal restrictions on multiple accounts apply. You are allowed to have multiple accounts, but:
- there is no official support for that; it's down to you to ensure they're separated enough to not get merged
- if you're doing something with one that you would be prevented from doing with the other (evading question blocks/suspensions, voting on your own posts), that's abuse and your accounts are liable to moderator deletion/suspension
You can create multiple accounts from the same IP address, using separate email addresses (logins), so there is authentication at the account level that will supersede the ip address, for clean (unbanned) ip addresses. If you have an account ban, that will be linked with you ip address. There can be no account ban, if there's no account. A downvoted question, at worst will be deleted. This is different of course, with spammers and trolls, where abusive or spam flags on a post start a roll out for mod attention, who can then initiate an account ban.
The ban also takes in account the IP address. If you browse from a shared computer, or from a location that gives the same IP address to many end users, it's enough that another user who was banned or triggers the ban, will affect everyone else accessing from the same location.
The rep on a site where you have a migrated question, site Y, with or without an account should not make a difference to your account standing on site X. Most post bans are on a per site basis.
The premise in this quote, from here, applies.
Migrations are not possible if your account is banned from asking questions on the destination site. The question will simply be closed as off topic, but not migrated.
For you to get an across site ban on SE, you'd need to be doing something far worse than getting one downvoted question on one of the sites.
Also, the account on site Y which has the migrated question would have the same rules applied to it, as if you had voluntarily posted the question there, as opposed to migrating it. All the down votes from the original site X would be dismissed, the upvotes carry across with the question.
Reset votes on migrated questions
So subsequent downvotes would be applied to a migrated question in the same way as if the question had been asked originally on the migrated site. So the potential for question ban would follow the same algorithm.
If you're worried about a ban, perhaps consider editing the question to improve it.