Using the Advanced Bulk Editor will let you update multiple WooCommerce Products all at once. Here is a short video showing how to but Products On Sale for Black Friday.
Bulk Edit Sale Price:
1. Select the category to edit
2. Click the Get products Button
3. Click Show/Hide and make sure that you check Sale Start/End Date (If you want to set the dates)
4. Select the Products to Update
5. Click the "Bulk Update" Button
6. Under Sale Price, select the "Decrease by % (form reg)" option and enter 50 int he field.
7. Click OK
If you don't want to set a date range for the sale, then click Save Changes and your done.
To set the Date Ranges:
1. While the products are still selected (or select products to change) go to the bottom of the page
2. In the first selected Product, enter the Start Date.
3. Not enter the End Date
Click Save Changes.