Backers can't buy multiple tiers. You can only back a project once. :( You can increase or change a pledge to a different tier, but you can't buy more than one tier.
Viewing post in The Thorns of War Update #5 - Kickstarter Draft comments
WHAT?? NOOOOO. KS limits you to only ONE?? That's STUPID when I wanna give ALL my MONEY. Ugh... I guess I have to choose then. Unless BT makes a tier one below new 'Queen' one. Though, I did see that pledge payment isn't immediate withdrawal(?); if so, I'll go for highest tier even though I don't really NEED to design MC outfit(not that I'll hate it - just don't want it as much as the others). Either way, thanks for letting me know. <3
Edit: Confirmed. For those who don’t know, pledges aren’t charged until the project is successfully funded. There could be authorization holds, but if you’re wanting a tier you could possibly afford a month+ in the future, good to know.