It's a little fiddly on the iPad, which doesn't have a straightforward way to select a bunch of actions and edit them simultaneously like the Mac does. However, in some cases it can be done in a fashion that is more efficient than just editing each one.
Let's assume that all of these actions are in the Inbox.
Create another action in the Inbox, and set its context to be the context you want to assign to the other actions.
Select one of your actions, bring up the editor, and tap the Move button. Move it inside the action you just created. Tap Done. You've just created an action group with a context of the one you want to assign. Anything without a context dragged into that group will get the group's context.
Now tap the Edit button up at the top of the screen. Drag all of the other actions you wanted to assign the same context between the action you created and the action you moved. They will now all have the same context.
At this point, what you do depends on what your plan is for those actions:
- If you just wanted to assign contexts, you can drag them back out of the action group, then tap Done. The context should stay assigned. Delete the action you created when you've got them all moved out.
- If you wanted to move them into a new project, tap Done, then bring up the editor on the action group. Tap the Move button, then Convert to Project button.
- If you wanted to move them into an existing project, tap Done. Bring up the editor on the action group. Edit the project field and select the destination project. Tap Done. Next, go to that project, tap the Edit button at the top, and drag the actions out of the action group, and delete the action you created when you've got them all moved out. Tap Done.
I trust you can see how you would move a bunch of actions into a project without setting their context.
For just a couple of actions, it may not make sense to do this. I usually just do such tasks on the Mac, and I think I will continue to do so when it is convenient, but I used this technique to refile 177 items while writing this post, and it wasn't bad at all.