I thought you could do this at pretty much anytime, but I wanted to make sure.
Examples:
1) I make a battle challenge when all the lost souls are in sites and I don't have access. As a result of drawing a couple cards in the battle challenge, I draw Dragon Raid. Can I now add that to the battle to make it a rescue attempt?
2) I have Dragon Raid and New Jerusalem Site, and push New Jerusalem into battle. During the battle, I lose the New Jerusalem site. Can I now add Dragon Raid for site access?
3) I have Dragon Raid but frankly forget about it after I push my hero into battle (so I was inadvertently making a battle challenge). A) After my opponent presents a blocker,can I add Dragon Raid? B) If my opponent chooses not to block, can I now add Dragon Raid? (And if I can then I'm certain that this would allow him to re-decide if he is going to block.)
4) I push a hero into battle where I WOULD have site access if only my own site of the same color was not occupied. Can I now play Burial on my lost soul to empty the site and add it to battle?
As far as I recall, all of the above work, but it came up again at today's playgroup meeting. Thanks for your help.