Lilypond: Instrument part transpose with several key signatures

Question

For example, I have a very long clar.nets part starts in Fis-dur and ends in G-dur written in concert pitch. How can I apply transposition to them without causing weird key signatures at the beggining or at the end?

ClarinetI = \relative c' {\key fis \major
fis8 gis ais b cis cis cis4 |
\key g \major
g8 a b c d d d4
}
ClarinetII = \relative c' {\key fis \major
dis8 eis fis gis ais ais ais4|
\key g \major
e8 fis g a b b b4
}
\new Staff \with {instrumentName = "clarinets in concert"}<<
\partCombine \ClarinetI \ClarinetII
>>
\new Staff \with {instrumentName = "clarinets in B"}<<
\transpose bes c' \partCombine \ClarinetI \ClarinetII
>>

I want resulting part look like this:

Generally, as I'm exporting the score from Reaper midi — I can add some Python logic into the export process, but currently I'm inside the production and need to works with the exported parts as they are.

PS I've tested MuseScore against my example and...

Answer 1

As a temporary fix, I've wrapped Fis-dur part into enharmonical transpose statement. But I would like to see more reliable and complex solution.

ClarinetI = \transpose c c' { \transpose fis ges {\key fis \major
fis8 gis ais b cis' cis' cis'4 }|
\key g \major
g8 a b c' d' d' d'4
}
ClarinetII = \transpose c c' { \transpose fis ges {\key fis \major
dis8 eis fis gis ais ais ais4|}
\key g \major
e8 fis g a b b b4
}
\new Staff \with {instrumentName = "clarinets in concert"}<<
\partCombine \ClarinetI \ClarinetII
>>
\new Staff \with {instrumentName = "clarinets in B"}<<
\transpose bes c' \partCombine \ClarinetI \ClarinetII
>>