In objection.js, how to make `.modifyGraph` return alias or boolean?

Question

I have the following query

UserReaction.query().where({
        target_id: userId,
        type,
      })
        .withGraphFetched('[user.[user_data, reactions]]')
        .modifyGraph('user.reactions', builder => {
          builder.where('user_id', '=', userId)
        })

This works and returns what I want, except I want user_reactions.user.reactions (the item in the .modifyGraph) to be a boolean with a different alias (currently it returns as an array of objects).