There is no reliable way for INK WebApp to force Metamask to show customized tokens, but it provide several conveniences to help users get around this issue.
A user will have the connected wallet displayed on the upper right corner, and when the addresses of the wallet is clicked it is copied for pasting.
A user can go to a DAO's Exploring View, clicking the name of the DAO's governance token will activate Metamask to import that token into the user's wallet.
A user can go to a DAO's Exploring View, clicking the name of the DAO's Badge will activate Metamask to import that badge token into the user's wallet.
On any mainnet, user can always import USDT or USDC from Metamask.
To deposit assets into a DAO's treasury vault, the DAO must have set up its Treasury first. The user can go to the DAO's Exploring View, and expand the DAO Activities on the left panel and select the "Treasury Balance", which will show the address of the treasury vault on the right panel. Clicking on the address will copy this address and allow the user to paste it to make deposits.