Do I have to add fringes to every line by hand?

Configure fringes on one Cost Item, then duplicate that line for every further position with Duplicate Selection (⌘D). The copy carries the AddOn with it, and when the rate lives in a Variable, one edit moves every line that uses it.

You choose the route that fits the budget. They also work together.

Route 1: configure one line, duplicate it

Open Insert, then AddOns, and drag the fringes card onto the first Cost Item.
Expand the strip and set the rate and the mode. The mode button sits at the start of the sentence line: Unified applies one rate to everything the AddOn covers, Individual gives each item its own rate.
Select the line and press ⌘D. The duplicate arrives with the same AddOns, and its name gains the suffix (Duplicate) so you can see what to rename.
Rename each copy and set its Amount, day count and Fee.

Route 2: share one Variable

A Variable holds the rate in one place, and every AddOn linked to it follows it.

In the sidebar Variables tab, use + to open Create new Variable. Name it after the fringe, choose % Percentage, and enter the rate. Prepared cards create their own rate Variable the first time you use them in a budget.
Expand the AddOn on a Cost Item and click its rate field, which reads Number or @.
Type @, open the Variables tab, and pick the Variable.
Link each further AddOn the same way. Dropping the same prepared card onto another Cost Item reuses the Variable it created, so the whole budget starts on one rate.

A renegotiated deal is then one change in the Variables tab. Every linked AddOn recalculates, and so do the Section subtotals and the Total. See A contribution rate changed this year. How do I update every line at once?.

Good to know

A rate field holds either a Variable chip or a typed number. If you type a number into a linked field, that line stops following the Variable. Type @ and pick the Variable again, and the line follows it again.
An AddOn belongs to one Cost Item, which is what lets a duplicated line carry its fringes with it. For one uplift across a whole department, see Can I put an uplift on a whole chapter instead of every line?.
Unified and Individual keep separate settings. A rate typed in one mode does not appear in the other, so set the rate in the mode you plan to keep.
Several percentage AddOns on one line each work from the same starting amount and do not compound. To apply one on top of another, tick that AddOn in the selection menu.