The documentation on dtexec Utility (SSIS Tool) says the following:

/Set propertyPath;value

(Optional). Overrides the configuration of a variable, property, container, log provider, Foreach enumerator, or connection within a package. When this option is used, /Set changes the propertyPath argument to the value specified. Multiple /Set options can be specified.

At first sight this works like a charm but as soon as your value has a space dtexec seems to get confused 🙁 It took me a couple of websearches to find a post that suggests the following:

dtexec /SET \Package.Variables[User::TheVariable].Properties[Value];'’; space’';

It seems that this works like a charm 🙂 Because i am lazy i wrapped this in a powershell function:

function PackageOption()
{	  
	param($name, $value);
	"$name;\`"\`"$value\`"\`"";
}  

And now you can use it as following in your deployment script:

$TheVariableOption = PackageOption -Name "\Package.Variables[User::TheVariable].Properties[Value]" -Value "some thing";
&dtexec /File "$package" /Set $TheVariableOption;