To update custom fields of all resources, you need to go to edit the resource, go to custom fields, update it and save. Then do this one by one for all resources.

Suggesting a faster bulk update for custom fields, such as having the possibility to add custom field columns within the list view of "Manage Resources" or exporting all resources with custom fields, updating the custom fields manually in i.e. Excel, then importing it again.

We're using the custom fields to keep track of the overtime and travel days which is updated each month, so it's a tedious process.

In my case, I'm voting for the custom resource field, I don't know if this could be useful also for the custom project field.