There are 2 options -- with one you make 1 change and it applies to all items in your account and there would be no override formulas (meaning it's easier to make mass changes again later. With the other, you change selected items and cause them to have override formulas.
Repricing ALL items in your account to 1 formula
This would be done in your default formula settings.
1. Go to Settings --> Ebay --> US or UK (depending on the platform you are selling on)
2. Scroll down a little and look for Calculating eBay's Selling Price
3. Click the Switch to Wizard Button
4. Enter new values into the wizard here. (Use Estimate Price to test the formula)
5. Click Close
6. Save your settings.
7. Then you can go to My Items --> Batch Options --> Force Reprice All Items
Doing the steps above will apply to all items in your account that are NOT overridden. If you have overridden your items intentionally (by editing them and applying an override formula) or if you were listing with hydra and you listed with an override or if the default formula settings in hydra were different than they were in skugrid at the time of listing, then changes to your default settings would not apply. It would only apply to items where an override does not exist. If you need to remove all override formulas go to My Items --> Batch Options --> Remove all Per Item Formulas. Then you can go to My Items --> Batch Options --> Force Reprice All Items This will place all items in queue to be repriced. Expect it to take up to 30 min - 1 hr (it really depends on amount of listings and server load at the time).
NOTE: If you are listing with hydra and make changes to your default formula in skugrid, you should make the same formula changes in your hydra settings so that your items do not all come over with override formulas.
Repricing Selected Items to 1 Single Formula
You also have ability to select items and reprice them with a different formula than the rest by doing the following.
1. Put a check mark next to the items that you would like to change.
2. Go to Multi-Item Actions
3. Select Add Formula
4. Enter values into the wizard popup and follow the prompt to apply it
5. This will cause all selected items to be given the same Override Formula (changes to your default formula settings will no longer apply until the item is set back to using default formula).
6. Now since the items are still selected, you can click Force Reprice Selected to cause the selected items to go into the queue to be repriced. It will take some time and is not an immediate change.