Can I have a custom visual component (a slightly modified TSpeedButton) that could be dragged to form and exists across some project only, not requiring to be registered Delphi-wide? I also do not want to emulate button using TFrame. It should not be available to other Delphi projects.
Unfortunately, no. Using the component at design-time requires putting it into a package that is installed into the IDE. However, you can enable/disable installed packages on a per-project basis as needed.