I had tried to install software Paint.Net v2.5 but found a permissions
problem re Admin-level user (called "Admin-1") accessing registry keys in the
HKLM branch. This is the first time this type of install problem has
occurred and it was suggested that some aggressive antispyware, antivirus, or
similar program may have changed permissions, but I would not know.

Question:
If I add the following users:
Administrators (full control, read)
Admin-1 (full control, read)
SYSTEM (full control, read)
to the registry key:
HKEY_LOCAL_MACHINE\Software
will I mess up permissions in any or every program, since permissions are
inherited? I would have assumed the above suggested changes would make no
difference because the existing permissions on the registry key
"HKEY_LOCAL_MACHINE\Software" is:
Everyone (full control, read)
Do you suggest making the above changes?
Do the permissions in the registry key "HKEY_CURRENT_USER\Software" matter
in this regard?

Computer:
1.47 Ghz Athlon
OEM XP Home + SP1 + all updates
256MB shared ram
NTFS file system
MS Net Framework 1.1 + hotfix KB886903

Following are some existing registry key permissions (as far as I know, the
"deny" checkboxes are all unchecked, for all users, for all keys):

HKEY_LOCAL_MACHINE:
Administrators (full control, read)
Everyone (read)
RESTRICTED (read)
SYSTEM (full control, read)

HKEY_LOCAL_MACHINE\Software:
Everyone (full control, read)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer:
Administrators (full control, read)
CREATOR OWNER (special permissions: full control subkeys only)
SYSTEM (full control, read)
Users (Read)

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Applications\i _view32.exe:
Administrators (full control, read)
Admin-1 (special permissions: full control this key only)
CREATOR OWNER (special permissions: full control subkeys only)
SYSTEM (full control, read)
Users (read)

****Serif Photoplus 6.0 always says "failed to update system registry" when
opened by Restricted User but works fine:
HKEY_LOCAL_MACHINE\Software\Serif
Administrators (full control, read)
Creator Owner (special permissions: full control subkeys only)
Users (Read)
SYSTEM (full control, read)

****When Restricted User clicks to close program HTML Help Image Editor
(part of Microsoft's HTML Help Workshop), it always says "cannot open the
file C:\Windows\flash.fpr", but program works fine:
HKEY_LOCAL_MACHINE\Software\Microsoft\HTMLHelp
Administrators (full control, read)
CREATOR OWNER (special permissions: full control subkeys only)
Admin-1 (special permissions: full control this key only)
Users (Read)
SYSTEM (full control, read)

****For Admin-level user Admin-1, on key HKEY_CURRENT_USER and on key
"HKEY_CURRENT_USER\Software":
Administrators (full control, read)
Admin-1 (full control, read)
RESTRICTED (read)
SYSTEM (full control, read)

****For Restricted_user-2, on key HKEY_CURRENT_USER and on key
"HKEY_CURRENT_USER\Software":
Administrators (full control, read)
Restricted_user-2 (full control, read)
RESTRICTED (read)
SYSTEM (full control, read)