The standard way to change Label Object text is to link it to a gate and set Label property using Template Builder.
Use template objects manipulation by code as last chance.
Only some of the objects properties are supported by TObjSetProperty_ and TObjGetProperty_. Supported properties (for each object) are listed in Template Builder online help.
If can not change the background/foreground color of a Label, use a StatusBar instead. No code is necessary, you can done all using gates and Template Builder.