Yes! Anything you put in now over your pledge amount will be available to spend in the pledge manager. You will also be able to add more money to that amount in the pledge manager. The pledge manager will be open shortly after the kickstarter is final.
Best way is our website: http://www.sfr-inc.com/
Also our Facebook page: https://www.facebook.com/DragonDice
For Slack, send us a message with your email, and we'll send an invite.
Facebook fan group: https://www.facebook.com/groups/418460488199950
The pledge manager will close about one week before we start shipping. The exact time depends on when all the product we are having manufactured gets to us. We will give everyone a couple of weeks of notice before the close the pledge manager.
When you pledge or update your pledge, kickstarter fills in the amount with the cost of your pledge. If you change that amount to a larger number, that is the amount for later add-ons. For example: you pledge at Chimera level. It puts $100 in the amount. If you want to add-on a Hardcover rulebook (cost $20), just change that $100 to $120.
Don't see the answer to your question? Ask the project creator directly.