Should learn from Tejas project management experience. With proposed changes its basically a whole new aircraft and should be treated as such. You only try to build something yourself if, your desired solution doesn't exist, no one is willing to sell what you want or you believe you can make it cheaper. It will delay AMCA as well since will take up engineering resources that could have been diverted there. These specs might sound ok for now but problem with InAF/HAL is that by the time its flying in 2028-30 InAF will revise the requirements based on new threats and technology developments. This is what happened with current variant.
Should rather concentrate on current Mark-1A airframe, its future upgrades and AMCA.
Just theoretical but Novi Avion a cancelled project by Yugoslavia could have been restarted by HAL. It had technical assistance France so looks similar to a single engine Rafael.
en.wikipedia.org