The segments package provides Unicode Standard tokenization routines and orthography segmentation,
implementing the linear algorithm described in the orthography profile specification from
The Unicode Cookbook (Moran and Cysouw 2018 
Create a text file:
$ echo "aäaaöaaüaa" > text.txt
Now look at the profile:
$ cat text.txt | segments profile
Grapheme frequency mapping
a 7 a
ä 1 ä
ü 1 ü
ö 1 ö
Write the profile to a file:
$ cat text.txt | segments profile > profile.prf
Edit the profile:
$ more profile.prf
Grapheme frequency mapping
aa 0 x
a 7 a
ä 1 ä
ü 1 ü
ö 1 ö
Now tokenize the text without profile:
$ cat text.txt | segments tokenize
a ä a a ö a a ü a a
And with profile:
$ cat text.txt | segments --profile=profile.prf tokenize
a ä aa ö aa ü aa
$ cat text.txt | segments --mapping=mapping --profile=profile.prf tokenize
a ä x ö x ü x
>>> from segments import Profile, Tokenizer
>>> t = Tokenizer()
>>> t('abcd')
'a b c d'
>>> prf = Profile({'Grapheme': 'ab', 'mapping': 'x'}, {'Grapheme': 'cd', 'mapping': 'y'})
>>> print(prf)
Grapheme mapping
ab x
cd y
>>> t = Tokenizer(profile=prf)
>>> t('abcd')
'ab cd'
>>> t('abcd', column='mapping')
'x y'