In Addition to the prior suggested way you can manage it the following way:
1. Make a copy of existing Page 31 (Item List) to new page e.g. 50000 Item List SO via save-as
2. Insert in new copied Page (e.g. 50000) on OnOpenPage Trigger the following Code
SETRANGE(TempBlock,FALSE);
If you want to keep the filter uneditable you can hide it via FILTERGROUP
3. In Page 46 on Field "No." go to Properties and set as DrillDownPageID and LookupPageID this new created page e.g. 50000
Now you only have this filter criteria in the additional page which is only accessible through the Sales Order Subform. Please remember that any further customization on standard page 31 might need to be added to this new listpage (e.g. 50000)
To avoid the usage of Tempblocked items please add the following Code to field "No. - OnValidate" of Page 46 (Item is a new global Record on Table 27):
No. - OnValidate()
IF Type = Type::Item THEN BEGIN
Item.GET("No.");
Item.TESTFIELD(TempBlock,FALSE);
END;