If i have a team that is short of being a theme team (Nova Corps keyword) by one figure. If that figure successfully uses the Nova Helmet and is granted the Nova Corps keyword do I also gain theme team re-rolls?

No, whether or not a force is a themed team is only checked at the beginning of the game. If you pick it up in the middle of the game, it won't be a themed team.

Although, this does bring up a different question: If a bystander on a Nova Corps themed team picks the Helmet, would they now be able to use themed probability control rolls, since they gained the keyword, or would the bold part below still prohibit them?

Thanks for the clarification. I guess it doesn't specify whether they cant be given keywords or not.

They still would be unable to use the TTPCs as those are bonuses.

I've got a somewhat related question on the Nova Helmet. If I'm playing the Nova Corps ATA and the Nova Helmet, and one of my non-Nova Corps figures picks up the helmet, do they gain the ATA? The situation where I think it would matter if is my opponent is playing the new JLA ATA, and has picked the Nova Corps team as his target for the attack boost. Would his JLA pieces get the +1 attack against my Nova Helmet wearer?

They would not gain the ATA. The ATA is part of your constructed Force and is assigned to characters as part of your Constructed Force.

This is actually not necessarily the correct answer.

This falls into the category of AEs and ATAs which is currently under discussion.

Huh?
I have a Nova Corps themed team which includes a bystander and the Nova Helmet. The bystander picks up (acquires? what's the official term?) the helmet. He now posesses the Nova Corps keyword. What's stopping him from using the TTPC?

Apparently, TTPC is considered a bonus of a theme team. From Rulebook, pg 21, last sentence of the first paragraph of the "Themed Teams" section:

"Bystander tokens can be included in your force although they do not have keywords, but they are not considered “characters” for the purpose of bonuses or counting characters for qualifications described below."

Though the Bystander wouldn't count toward determining the bonus I would think that once they pick up the helmet they could use a TTPC if you already earned them for your team; much like an AE that loses a keyword can no longer use it.

In the statement you quoted, there is a quote from the rulebook, page 21:

"Bystander tokens can be included in your force although they do not have keywords, but they are not considered 'characters' for the purpose of bonuses or counting characters for qualifications described below."

There are three bonuses that you get for having a themed team:
- Canceling a BFC
- +1 to initiative roll for each character
- Themed team PCs

Regardless of picking up the proper keyword, the bystander is still a bystander, so it still doesn't count as a character to use a TTPC.

Harpua that would be a very interesting ruling indeed if it becomes that they would gain the ATA mid game simply by picking up the Helmet. I can see how this is similar to a Wild Card choosing an ATA, yet is is also different.

What I don't get is how this is related to AEs and ATAs. Am I missing something that I shouldn't be?

Ah, I misunderstood bonus - thanks for the clarification

edit: I misunderstood it to mean whether or not you gain the theme pcs, not whether or not you can use them (which I thought was only determined on keywords)

At the moment there has not been a final ruling on how AEs work with ATAs.

Something like Norman Osborne or Diana Prince AEing into the Green Goblin or Wonder Woman is simple enough. Norm has the keyword and paid for the Thunderbolts ATA. GG also has the keyword, so he can continue to use it.

Somthing like Hulk Bruce Banner AEing into the GG Hulk (#027) is a different matter. Bruce does not have the Defenders keyword. Hulk does have it. (Assume that the The Order ATA is in play.) We simply don't have a ruling yet about this is to work.
There are several possibile outcomes:
1) At the beginning of the game the ATA is paid for by paying 3 points for each figure showing the Defenders keyword at that time. After the AEing, Hulk gets to use it for free.
2) At the beginning of the game, you MAY pay 3 points for Bruce in addition to the 3 paid for everyone else. After the AEing, if you paid the 3 points, you get to use the ATA, but if you didn't pay, you don't use it.
3) At the beginning of the game, you MUST pay 3 points for Bruce in addition to the 3 paid for everyone else because he has the potential to get it. After the AEing, Hulk can use the ATA.
Etc.

There are several ways that this may play out in the end. What you said might end up being the correct answer, but at this time there is no official answer.

This sounds correct.

Picking up the helmet then adding the ATA would change the point total of you force mid game. How is there any discussion other than that?

Edit: nevermind, just saw your possibile outcomes.