From the question, it is unclear that you want to alter the schema of wiki page library or want to update the item metadata columns. Since you mention `Modified By` or `Modified Date` should not update, I guess here you are working on item metadata update.

In PowerShell you can SharePoint CSOM. They key point here is to use `SystemUpdate()` method rather than `Update()` method. Read more on this at https://docs.microsoft.com/en-us/previous-versions/office/sharepoint-server/ms461526(v%3Doffice.15)

But the downside of above workaround is it still triggers the Event Receivers and WF. https://sharepoint.stackexchange.com/questions/222189/stop-workflow-triggering-when-systemupdate-is-called