Will we be able to open a theme made by somebody else and modify it using Themeframe?

If it was made with ThemeFrame, and the settings file (i.e.: my-custom-theme-3.txt) is available, yes.

These small text files (~30-60 Kbyte) contain all the CSS and layout settings and can be opened in another Themeframe installation. There, you could change CSS or layout settings and export a new theme.

Themeframe does currently not export complete .ZIP files with i.e. custom images of the theme and static CSS, JS and PHP template files, basically all-in-one, complete standalone themes that you just need to unzip and upload, like any other theme. I will include this later on but this functionality will probably require that a the PHP ZIP extension is installed on the web hosting server, or that the hosting account runs on PHP 5.2+, where ZIP is integrated.

Ah. OK. I was envisioning opening some third-party theme and totally redoing it. But if creating a totally new theme using TF is going to be as simple as it seems from the videos, who needs that capability?