Reproduction steps:
1. Create a new project
2. Window > Package Management > Package Manager > + > Create Package…
3. Enter any package display name, select newly created package and press “Export” button
4. Select any Organization in the Export Package window and press “Export” button
5. Remove the package (Manage > Remove)
6. Reinstall exported package (+ > Install package from tarball…)
7. Manage > Customize
8. Open Manage > Edit Manifest, change Technical Name field in the Inspector, press “Apply” button and observe the Console

Actual result: “Assembly with mane ‘…’ already exists” errors and “GUID […] for asset ‘…’ conflicts with:  ‘…’ (current owner) Assigning a new guid.” warnings are thrown
Expected result: No errors or warnings are thrown

Reproducible with: 6000.3.14f1, 6000.4.6f1, 6000.5.0b7, 6000.6.0a4
Couldn’t reproduce with: 6000.0.74f1 (No “Create Package” option)

Reproduced on: Windows 11, macOS Tahoe 26.4 (M4)