When Forge generates code it formats it with the current Forge [Eclipse-based] formatter: 3 spaces indentation and opening braces on the next line. As mentioned by George in the mailing list, if you develop an addon, it is possible to control that via the Roaster API by calling Roaster.format() passing as an argument the Eclipse formatter profile XML.

However, it would be a good idea if I am just a Forge user to be able to configure the already existing addons that generate code (e.g. the new entity command) to use a formatter that I have provided, so that the generated code follows the code conventions adopted in the project/team I work in