I have a cousin in BP and a son-in-law in NG. Also just this past Tuesday spoke with a State Senator on another topic and he brought up Texas NG going to the border. What you stated about the roles is accurate according to those sources up to now.
As I understand it now, in Texas anyway, roles could evolve to more NG action. NG will also be stepping up to do some patrols (after training for this) they can’t arrest illegals but will be able to detain and call BP for the legal work. That was my understanding from my senate conversation, any inaccuracy would be my fault because this was not my main topic of concern in the conversation so my recollection could be goofy.
This alert just popped up, looks as though NG duties may be involving more than just support, from article at link:
Trump slams California Gov. Brown for sending ‘do-nothing’ National Guard to border
President Trump warned California Gov. Jerry Brown that he’ll cut off federal funding for the deployment of California’s National Guard if the governor insists that the troops “do nothing” instead of enforcing immigration laws.
“Governor Jerry Brown announced he will deploy ‘up to 400 National Guard Troops’ to do nothing,” Mr. Trump tweeted. “The crime rate in California is high enough, and the Federal Government will not be paying for Governor Brown’s charade. We need border security and action, not words!”
snip
I don’t wish for any of our folks to get hurt, but what I’d love to see the guard used for is to engage the cartel convoys that currently drive trucks across our border with apparent impunity. Get that first combat under our belt, let it be the camel’s nose under the tent and then go to war with these mother f*ers.
And if they scream Posse Comitatus do it on the Mexican side of the border.