Schedules are not built from templates.
When you create a 'New' schedule, you have the option to 'Duplicate' an existing one - but they will be separate schedules once created.
So if you have created 20 schedules and you want to make changes, you will need to do it for each one.
The custom text may be solvable though.
You say there is information that you can't get from Archicad.
Have you looked at 'Classifications' & 'Properties'?
Briefly you can classify elements and you can have properties associated to those classifications.
The properties can have undefined. default or custom values.
So you can set a default value for a property, associate that property with a 'Window' classification and all windows will get that property value once you classify them as a 'Window' (you can override it in individual values in each window if you want to).
You can schedule these properties just by adding them like any other field in the schedule.
Barry.
One of the forum moderators.
Versions 6.5 to 27
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