How to affect UDA to members in account dimension ?

Hello,

We need to affect UDA to members in account dimension thanks to the webform, where :

1. a user can input value "1" in a particular cross of dimensions, including member of account dimension
2. then the groovy rule beside could assign the UDA to the member in account dimension

Exemple of webform :

⇒ in this form when a user puts "1", we need a groovy rule which assigns UDA to the accounts indicated on the left…

Could you help us to indicate ways to do that ?

We know that we can create members in any sparse dimension, which will correspond to UDAs, and then with groovy rule assign the UDA to members of account dimension thanks to these members in sparse dimension.