Hey does anyone know if custom transaction line fields can be mass updated at all? Thanks 🙂

Not via the Mass Update function (that only works for header fields), but for most transactions, you should be able to update those via CSV. Which transaction type(s) are you trying to update this field on?

I am using an estimate in order to use an advanced pdf/html template to send to customers (will be using a workflow to mass send these out) and need to update a check box based on specific criteria on an item line by line basis rather than the whole document so was hoping mass update would work to prevent having to upload it again!