There's no reason you can't make them, but there'd be some problems in getting HTC to accept it.
The Yak-7 is an early war plane, which was a single-seate fighter version of the two-seat trainer plane.
Early days in the Eastern front, the supply rate of the Yak-1 couldn't follow its demands, so the VVS coped by modifying the two-seat Yak trainer Yak-7UTI.
The first Yak-7s were modified from Yak-7UTIs, and IIRC, after the first initial modifications the factories that assembled UTI trainers were now standardized to produce Yak-7s from the start. The Yak-1s developed into the Yak-1B, and then became the Yak-3 - this line was known as 'light Yaks'. The Yak-7s developed into the Yak-9, and finally the Yak-9U, which line was known as 'heavy Yaks'.
The performance difference between a Yak-7 and a Yak-9 is huge, not to mention that it also has a very different exterior.
