Hi partner,
This is achievable.
There are two simple ways, 1. export and modify the data and then import it, 2. use an on-demand workflow.
Here I introduce the first way, export and import data. We need to batch modify the "Sales Stage" field in Excel.
1) If you already have a personal view showing the opportunity records to be modified, open Advanced Find, use this view, click Edit Columns, and add the "Sales Stage" field.

Click Result, then click Export Opportunities > Static Worksheet. The Excel file will be downloaded.

If you don't have a personal view showing the opportunity record you want to modify, create this view first and then add the "Sales Stage" field.
2) Open the Excel file and change the value of the "Sales Stage" column.

3) Open an Opportunity view, click Import form Excel. Upload the modified file.

After finishing import, go to Advanced Settings > Data Management > Imports to see the import result.
