I'd like to set my own targets for nutrients, can I do this?

Yes. If you wish to manually adjust your nutrient targets, here's what to do:

In the app

Tap the blue menu button to the right of the search bar, select Nutrient Goals > Set My Own Goal. Enter either the grams or percentage figure for each nutrient. When done, make sure you scroll down and press the green Apply Changes button to save your targets.

On the website

Go to your Food Diary page and click on the Settings link above your diary. Next select Set a nutrient goal, then Set My Own. Click on either the grams or percentage figure for each nutrient to enter your own value. When done, make sure you scroll down and click the green Apply Changes button to save your targets.