How will DISM /Online /Cleanup-Image /RestoreHealth affect my current configuration?

Will I need to start over?

No, please see the below.

If I use Dism /Online /Cleanup-Image /RestoreHealth, how will it affect the currently installed software or any Windows configuration I might have changed?

It doesn't affect any installed software, as /Cleanup-Image deals with the Windows Component Store, not third-party programs, nor any customizations made to the OS:

• The Component Store [%WinDir%\WinSxS] maintains a backup copy of all Windows system files and SFC and DISM manage two separate, vital pieces of the Component Store and OS, with SFC relying entirely upon what DISM manages:
  • DISM has two functions SFC relies upon, /StartComponentCleanup and /RestoreHealth, with /RestoreHealth relying solely upon /StartComponentCleanup
    • /StartComponentCleanup: Cleans the Component Store of any broken hard links
      It's imperative folks on Insider Builds run this regularly due to the frequent updates
    • /RestoreHealth: Verifies and fixes any corruption in the Component Store by verifying its system file backups against known good copies from the Windows Update servers through hash comparison; while an offline method does exist [below], it may not always fix the corruption
      • Windows 7: SUR [System Update Readiness] tool is used in lieu of this, as DISM did not have this functionality until Windows 8
        
        
  • SFC always assumes the Component Store is not corrupted and is why the DISM /RestoreHealth parameter (Windows 7: SUR) should always be run prior to SFC; not doing so allows a corrupted Component Store to potentially replace a good system file with a corrupted one or fail to fix corruption within %WinDir% altogether
    • /ScanNow: Verifies and fixes any corruption within %WinDir% by verifying against the known good copies within the Component Store through hash comparison

• DISM and SFC must be executed in the order listed, as each relies upon the preceding step:
  ^{(Windows 7: skip to #3)}
  1. +R → Open: PowerShell → Ctrl+Shift+OK

     # Windows ≥8:
       # Online (while booted to Windows):
         Dism /Online /Cleanup-Image /StartComponentCleanup
     
       # Offline (while booted to WinPE/WinRE):
         Dism /Image:"D:\Windows" /Cleanup-Image /StartComponentCleanup
         # C: is usually not the drive letter in WinPE/WinRE
         # To ascertain: DiskPart → Lis Vol → Exit
     

     The Component Store should always be cleaned prior to running Windows Update, after an issue with Windows Update, and at least once a month, as it becomes dirty over time from updates occasionally breaking hard links
     
     

  2.  # Windows ≥8:
        # Online (while booted to Windows):
          Dism /Online /Cleanup-Image /RestoreHealth
     
        # Offline (while booted to WinPE/WinRE):
          Dism /Image:"D:\Windows" /Cleanup-Image /RestoreHealth
     

     Requires an internet connection, else the offline method will be required:
     • Use the install.esd||install.wim from the Windows Install ISO for the installed version (v1909, v2004, etc.):
       1. Create Windows 10 installation media → Download tool now → install on another PC
       2. Mount the ISO and determine the installed OS index [image] from the install.esd||install.wim:

          Dism /Get-ImageInfo /ImageFile:"Z:\sources\install.esd"
          

       3. Specify the index number at the end of the /Source parameter:

          # Online (while booted to Windows):
            # ESD:
             Dism /Online /Cleanup-Image /RestoreHealth /Source:esd:"Z:\sources\install.esd":6 /LimitAccess
          
            # WIM:
              Dism /Online /Cleanup-Image /RestoreHealth /Source:wim:"Z:\sources\install.wim":6 /LimitAccess
          
          # Offline (while booted to WinPE/WinRE):
            Dism /Image:"D:\Windows" /Cleanup-Image /RestoreHealth /Source:esd:"Z:\sources\install.esd":6 /LimitAccess
          

          
          
  3. Windows 7: Run the SUR tool
  4. Reboot; if errors are found, review %WinDir%\Logs\DISM\dism.log from the bottom up
     ^{(Log files are easier to read and sift through via the Log syntax in VS Code)}
     • Windows ≥8: %WinDir%\Logs\DISM\dism.log
     • Windows 7: %WinDir%\Logs\CBS\CheckSUR.log (How to fix SUR errors)
       
       

  5. # Online (while booted to Windows):
       Sfc /ScanNow
     
     # Offline (while booted to WinPE/WinRE):
       Sfc /ScanNow /OffBootDir=D:\ /OffWinDir=D:\Windows
       # C: is usually not the drive letter in WinPE/WinRE
       # To ascertain: DiskPart → Lis Vol → Exit
     

     
     
  6. Reboot; if errors are found, review %WinDir%\Logs\CBS\CBS.log from the bottom up
     
     

Run first sfc /scannow before doing DISM.

Theoretically, your configuration should not be affected by either of these commands. But in case of advanced degradation of your system, the repair itself might cause further damage. The chances for that are very slim, but do not skimp on backups before starting.

I suggest having a look at this answer of mine.