No, you can easily mod it. Look for the line
SHORT_TECH_APP_INFANTRY_3_NAME
All "SHORT" lines in the localisation files contain the text displayed in the tech tree view.
edit: However, that works only if you have kept the original line
name = TECH_APP_INFANTRY_3_NAME
in infantry_tech.txt, otherwise you have to adjust the SHORT localisation accordingly.
SHORT_TECH_APP_INFANTRY_3_NAME
All "SHORT" lines in the localisation files contain the text displayed in the tech tree view.
edit: However, that works only if you have kept the original line
name = TECH_APP_INFANTRY_3_NAME
in infantry_tech.txt, otherwise you have to adjust the SHORT localisation accordingly.