1. create a admin shortcut for catia
e.g. E:\R17\intel_a\code\bin\CNEXT.exe -env CATIA_P3.V5R17.B17 -direnv "E:\R17_ENV" -nowindow -admin
2. Tools -> Standards At Category select drafting, at file select your Standard(e.g. iso.xml)
3. In the tree (at firs level) go to Dress-Up, select Symbols
4. Select the arrow u want to change
5. Change the Length and/or Angle
6. Repeat steps 4 and 5 for all elements u want to change
Important!!!
before u change the standard i suggest to create a folder eg E:\R17_COLLECTION_STANDARDS
In Catia Enviroment file change the line CATCollectionStandard=E:\R17_COLLECTION_STANDARDS
because after u change the standard Catia will create a copy of that in the folder mentioned above