Q: How do I stop a legacy application from triggering User Access Control? Why is UAC being triggered?

A: Windows has heuristics that detect installation programs that will trigger UAC. Usually a legacy application triggers UAC because Windows thinks the program is a setup image.

You can try removing words like "update," "setup," "install," and "patch" from the file name and its version information.

You can also disable install-detection through a policy modification:
1.Start the Local Group Policy Editor (gpedit.msc) (you could also modify a normal group policy object)
2.Navigate to Computer Configuration, Windows Settings, Security Settings, Local policies, Security Options
3.Double click User Account Control: Detect application installations and prompt for elevation (see Figure 1)



Figure 1: UAC uninstall


4.Set to Disabled and click OK
5.Close the policy editor

If you don't want to disable the application installer detection, you can use an Application Compatibility shim with the SpecificNonInstaller fix for the application executable, then deploy the generated shim file to the systems that use the program.