Hi, if you want to use more than 256 tiles then you can do it yes, you will just need to export the map data as 12bit or 16bit.
Exporting as 12bit or 16bit is currently only available (from CharPad) as text/asm/ascii but you can still use it in your project, just include the exported text as a link in your source code and build your project.
See the import/export menu items.
ps. unless you plan to dynamically load the data as binary from disk on the C64 at runtime, in that case you *will* actually need it in binary form I guess, CharPad can't currently do it but there are workarounds.