One change that might make this film a bit different from ANH is making the main goal of building the Starkiller to take out the Republic capital and their fleet and the whole purpose of entering the base and trying to destroy it is to prevent that.
A countdown graphic could be added to rank up the tension and the base would be destroyed but too late to save the targets so the footage of the core worlds being destroyed comes after the weapon has been destroyed. This would make the ending even more bitter sweet because not only have we lost Han but also the Republic government and defences all in the final act.
The capital being destroyed wouldn’t be an exact mirror of Alderaan but instead would play out like Yavin 4 being destroyed and a few survivors looking on in horror from escaping ships.
The First Order may have lost their big gun but it has done it’s main job. They won.