By Anthony Marshall - Newcastle United Managing Editor
Forward Armstrong, aged 18, will remain at the Ricoh Arena until Monday, 30th May, to include the play-off final, should the Sky Blues reach it.
The England Under-19 international joined Coventry last July and has been in prolific form, scoring 16 goals in 23 appearances to date.
Midfielder Bigirimana has seen the terms of his temporary deal with Coventry change under the extension.
The 22-year-old joined the promotion-chasers last November on an emergency loan deal, which was extended earlier this month. But he has now been moved to a standard loan, which runs until Thursday, 30th June.
Bigirimana has made five appearances for the Sky Blues and is yet to taste defeat.