Remove link between stage and probability

Stage and Probability cannot be un-linked, this relationship is hard-coded.The Probability value is always updated by a change in the Stage value, even if Probability is marked as read only on the page layout. Users with access to edit this field can override the value. As a workaround, it is possible to overwrite the Probability values according to the Stage.

The opportunity Stage affects the Probability values of an opportunity. As users change the stage of an opportunity, the Probability fields are automatically changed to the values specified during setup.

To update opportunity stages, go to:

• Classic: Setup | Customize | Opportunities | Fields, and select Edit next to the Stage field
• Lightning:  Setup | Object Manager | Opportunities | Fields and Relationships, and select Edit next to the Stage field

• To create a stage, click New. To edit a stage, click Edit next to the stage. Enter the stage name, probability of closing, type, forecast category, and description.
• To deactivate a stage and move it to the inactive list, click Del next to an active stage. On the mapping page, do not map the stage to another existing value; simply click Save. Inactive stages are stages that are no longer in use but may exist in older opportunity records. 
• To delete a stage completely, click Del next to an active or inactive stage. Map the deleted value to another active stage. If you do not map the deleted value, the stage is moved to the list of inactive stages.
• Click Reorder to change the sequence of picklist values.
• Click Replace to change the values of picklist fields in existing records.
• Click Printable View to open an easy-to-print list of your picklist values.
• Click Chart Colors and select an option to assign colors to picklist values for use in charts