All politicians alter their views on some issues to increase their likelihood of being elected. Some changes can only be made while in office. To get the opportunity to make real changes in areas important to them, politicians will often soften or change their stance on some issues until they are in office.
Trump views seem to fluctuate based on the amount of popularity he can gain. Since he has no experience with the military, and seems to have no specific fixed views, it is difficult to imagine how he would make decisions. On one day, he says he is against using force in the middle east, then states he would blow Iranian sailors who taunted American sailors out of the water. Coupled with his sensitive ego, he would be a very poor commander in chief.
Even if you allow that changing his views on gun control is a positive, his many negatives drastically outweigh that. He lacks the temperament to be a good commander in chief. He's too impulsive, takes the low road too often and can't resist the urge to taunt or shame those he feels disagree with him or treat him badly.
No, Trump's changing views on issues would not make him a good commander in chief. The fact that Donald Trump is constantly wishy-washy on his stance on important issues shows that he would not make a good president. It appears that Trump is unwilling to take firm stance on issues to avoid turning off his supporters.