1) Paragraph 7 of GPL3 explicitly allows developers to specify own conditions.
2) Copyright owner always has the possibility to re-license to anything he wants. GPL does not hinder that.
3) If rest of software uses GPL-licensed software, then, just like anything else, it should abide by its terms. There is special question why would you want different license from GPL. You want to use free libre software, but you don't want to follow its license. Then write your own version and use different license.