Add the following string entry to the Registry for the Alt-Plus method of entering characters:
Key: HKCU\Control Panel\Input MethodAfter a restart, you can enter Unicode characters by their hexadecimal value. [That's the alphanumeric number U+03c3 in the left part of the status bar in Character Map.] Hold down Alt and press the + key on the numeric pad and then the hex code for the character you want, without the leading zeroes if you like and then release the Alt key. Convoluted, huh? Here's a script that show's how to make light work of it with AHK: specialchar.ahk
String name: EnableHexNumpad
Value: 1
With this kind of script running, "/alpha" immediately becomes "α"
Bonus tip: you can use a "raw" hotstring for faster entries:
#IfWinActive HiEditor ; or whatever editor you use for editing AHK scripts
#Hotstring R
::<<::{alt down}{numpadadd}
::>>::{alt up}
#Hotstring R0
#IfWinActive
BTW, I should mention that AHK has a {ASC nnnnn} function for the alt-numpad method of entering special characters, but it has 2 main problems: it can enter only the decimal and not the hexadecimal code for a character (which is fine for ASCII and ANSI but less convenient for Unicode), and only certain applications using the RichText framework can interpret Unicode characters entered this way (decimal).