I agree that the lack of permanent links to search results in Soldatregistret is annoying. I have even had failures with the link to the search page, so I'm in the habit of using their general home page as my starting point:
https://www.soldatreg.se/sok-soldat/
I never noticed before, but there's a section in English. You can even do the search from a page that is (mostly) translated from Swedish.
As for Gustaf Lejon the more detailed information includes that he was enlisted in 1854 - which is relevant to the question about his name change - and dismissed in 1886.
The rest of the info makes it possible to find him in the muster rolls:
Regemente: Andra livgrenadjärregementet
Rote: Hultekil
Kompani: SKENNINGE
Socken: ÅSBO
Torpnummer: AL-07-0055
The roll for 1856 is the one describing his enlistment:
https://sok.riksarkivet.se/bildvisning/A0028293_00388
Generalmönsterrullor, Arkiv med löpande volymnumrering, SE/KrA/0023/0/318 (1856), bildid: A0028293_00388