That isn't full answer to your question, but may be helpful.
I have Geany not in english, I make translations of menu's fields on my own.
Geany has a feature: when you type special text and press Tab, the text is going to be replaced with another text.
It works by default for if, else, for, while, do, switch and try.
Configuration of this feature is in [Tools]/[Config files]/[snippets.conf].
After doing some changes, save file and click [Tools]/[Reload configuration].
I added two lines to section C++:
class=class %cursor%%block%;\n
struct=struct %cursor%%block%;\n
With block=\s{\n\t%cursor%\n}
It doesn't let you press { Enter or { Tab to get
{
//cursor
}
because {=anything is ignored, I don't know why.
What you can do? You can have some another text, replaced using {\n\t%cursor%\n}, or define keybinding inserting it.