adjust trimbox size according to page size

[Robbie]

I have a small question. is it possible to make a pistop workflow that wil increase the trimbox size if the total size is 5 meters ore smaller?
example: i have a document of 3000x4500 mm. Now we have to increase the size with 15 mm so it wil be 3015x4515 (and then with extra bleed)
This has to do with the stretch and shrink of the material we need to print on.
Not al the documents have the same size so it has to look at the trimbox and then increase it. But if the document size is more the 6 meters it does not have to do anything, and above 10 meters it has to decrease the size.

[freddyp]

There is an Action "Select by page size". With this Action you can select pages based on the size of one of the page boxes and when you modify one of the page boxes this will only happen for the selected pages.

[Robbie]

The idea is that now we have to manuaal input the size that we want (for example 3000x4000mm will become 3015x4015mm) I want to to this within a flow. It will see the size of the trimbox and ad 15 mm automatic and continue withe the rest of the flow to add lines/tekst

[freddyp]

The 'Change ... box" Actions have an option "Resize" that allows you to extend the current size by the values you specify, in your case 15mm. What you need is:
Select pages by size - greater than
Change trim box - Resize