Thianis

Unfortunately not. You have to start a new game in order to get it - but if it is still too difficult for you, you can very well skip the mission and complete your Normal run, then deal with Hard and retry Secret Mission 4 when doing your third run (this time selecting Normal again) - when you have all of Dante's abilities for both Alastor and Ifrit (not to mention the almost maxed-out health bar and maxed-out DT gauge), this mission should become easier by a magnitude.

Also, you would want to try to score Critical Hits against the shadows (i. e. wait until one of the shadows to do its Spear attack, then land on top of it and fill it up with lead. You will turn it red without having to attack its core), if necessary use your DT to speed up the process - and do your best to avoid the shadow's grab attack when it's red, because it's going to blow you up (best thing is to get airborne and wait for it to explode).

i think I have one more question. is there chapter select in this game? because im gonna miss out on the 3 beasts secret mission because I just know I wont be able to do it. with my current skill level.