[isaak]

Kobo Aura One Greek characters in extended keyboard: patch for libnickel.so in spoiler below.
I tried to uncomment "Enable uppercase for `ß` key (Top row, pos 7)" but it is not working. Mapped it to a symbol and all OK!
Thanks to GeoffR and the community!

Spoiler:

<Patch>
patch_name = `Greek Keyboard (Aura One)`
patch_enable = `yes`
# patch_group = `Keyboard alternatives`
#
## Replaces keys on the Extended Latin keypad.
#
# Aura One keyboard layout:
#
# Row:  Position
# ---:-----------
# Top: 0123456789
# 2nd: 0123456789
# 3rd: 0123456789
# Bot:  12345678
#  
# Untested: Enable uppercase for `ß` key (Top row, pos 7)
# replace_bytes = 6FFB40, 00 26, 01 26
#
# Replace layout sign Greek
find_base_address = `ÉÀÇ`
replace_string = 0000, `ÉÀÇ`, `ελ`
# Change keyboard layout
find_base_address = `š\0ž\0þ\0ŀ\0`
# Top row, pos 2-3
replace_string = 0000, `š`, `ό`
replace_string = 0003, `ž`, `ύ`
# Top row, pos 6
replace_string = 0006, `þ`, `ϋ`
# Top row, pos 9
replace_string = 0009, `ŀ`, `:`
#
find_base_address = `æ\0à\0è\0ì\0`
# Top row, pos 0-1
replace_string = 0021, `ý`, `ά`
replace_string = 0045, `ÿ`, `έ`
# Top row, pos 4-5
replace_string = 0000, `æ`, `ί`
replace_string = 0024, `œ`, `ϊ`
# Top row, pos 7-8
replace_string = 0054, `ß`, `-`
replace_string = 0060, `ij`, `_`
# Second row, left to right:
replace_string = 0003, `à`, `;`
replace_string = 0012, `á`, `ς`
replace_string = 0027, `â`, `ε`
replace_string = 0036, `ä`, `ρ`
replace_string = 0048, `ã`, `τ`
replace_string = 0051, `å`, `υ`
replace_string = 0006, `è`, `θ`
replace_string = 0015, `é`, `ι`
replace_string = 002A, `ê`, `ο`
replace_string = 0039, `ë`, `π`
# Third row, left to right:
replace_string = 000C, `ò`, `α`
replace_string = 001B, `ó`, `σ`
replace_string = 0030, `ô`, `δ`
replace_string = 003F, `ö`, `φ`
replace_string = 004E, `õ`, `γ`
replace_string = 005D, `ø`, `η`
replace_string = 0009, `ì`, `ξ`
replace_string = 0018, `í`, `κ`
replace_string = 002D, `î`, `λ`
replace_string = 003C, `ï`, `,`
# Bottom row, left to right:
replace_string = 000F, `ù`, `ζ`
replace_string = 001E, `ú`, `χ`
replace_string = 0033, `û`, `ψ`
replace_string = 0042, `ü`, `ω`
replace_string = 004B, `ñ`, `β`
replace_string = 0057, `ç`, `ν`
replace_string = 005A, `đ`, `μ`
replace_string = 0063, `ł`, `.`
</Patch>