Someone who desperately needs a livelihood and more funds, if it is permitted to buy lottery tickets, and to use the segulah of maaser, that if they win, they will bli neder give maaser from the amount that they actually receive, since most of the winnings go to various taxes.
It will probably be necessary to pay income tax as well.
Hashem should send everyone an abundance of parnossa, and no one should be needy. Before answering your question, it is quite skeptical if buying a lottery ticket is proper hishtadlus, as the chances of winning are extremely low, (one has more of a chance of getting hit by lightning, then winning the lottery.
But let’s say that you do win the lottery, at that point you would be obligated to give maaser, as you would no longer be considered poor. Therefore, I don’t understand what you mean by “using the segulah of maaser”. Additionally, a person that has money has to give maaser from all of their earnings, and not just from the money of the lottery ticket.
When calculating maaser, you would calculate only the money that you actually get, after all the taxes etc., because essentially that is not money that a realized profit.
One other point, before a person starts giving maaser, one should say that it is bli neder.