Interacting with Line Items in Transactions

Hello Everyone,

I was wondering if anyone can send me some sample code that interacts with line items in transactions.

Basically what I'd like to do is go through line items and refresh all item information based on the customer preferences, i.e. price levels.  I'd like to loop through the line items and update them according to these preferences, something I think the UI will do automatically.

Also there are other cases where I'd like to click on a custom check box in the line item and I'd like for another field on the same line to populate with something.