Well, you just need to call unicode_next_character all the time instead of saying s++, similarly for whitespace, similarly for asking whether a character can initiate or continue an identifier, etc. It does not change the basic nature of the task at all.

Here's a video of Rob Pike, developer of Go, talking about a lexer he built for the Go text/template package:

https://www.youtube.com/watch?v=HxaD_trXwRE

It supports unicode.

Hand-rolling a lexer seems pretty trivial to me. The code writes itself. A generator is a tool whose limitations you have to work around, be it for a lexer or a parser.

If you can't write a lexer by hand, just forget trying to write a compiler that does anything interesting, because the lexer is MUCH easier than any other part of the compiler.

There are a lot of reasons for this, but one of the basic ones is that the lexer does not need to interact in a complex way with the compiler's state. It is a relatively simple pipeline where characters go in one end and tokens come out the other.