is it possible to send merit for a future action ?
may the merit i do donating the 100$ - help this old lady cross the street etc go to X person ?
what about may the merit i do today go to X
what about the merit i do tomorrow go to X
Your giving are your merits, it's not possible to share ones merits in such way as thought. Even if giving the money direct to the lady to get a taxi to cross the street, the merits are yours. Taking (a gift) will be a debt, sometimes a debt torward Nibbana, torward those pulling in that direction, but mostly a debt binding to the world, and those after it.
But if the old lady, sees your deeds of sacrify, is able to rejoice with it, to take mentaly part on good deeds, then she has a share on you merits, and it's solvely up to her to take on the opportunity to take parts on your merits.
You good deeds will follow, as well as bad, there is no need to worry about that. Just a matter of crossing the right soil to ripe.
See more in regard of sharing merits and dedication:
"may the merit i do go to X"
Are your merits. If those who are dedicated are worthy of gifts, even very benefical gifts and wishes.
Anumodana, sharing of merits, is a way to fight ones stingyness and very seldom praticed by "modern Buddhist" since incapable to overcome stingyness. Only a person with firm confidence and those who have overcome maccariya (stinginess), e.g. noble ones, are really able to let others always take part on their good deeds. Many are thoses being slaves of envy of all kinds.
Places and people lacking in deeds of generosity and sharing merits, not used to mudita, for one after a better, should avoid such places, seek for association where such of doing and dedicating merits is practiced, jet hard to find in your grasped world, out of cause.
[Note: This is a gift of Dhamma, not meant for commercial use or other lower wordily gains by ways of exchange or trade]