I see no one is talking about this but I'm wondering if there is a way where you can edit the models like say copy from 0.500 to 1 in my current shape key so I can edit it easier similarly to how maya function works because in blender from what I've known so far (Since I'm still fairly new in this) keyframes can only be set for timing with already pre-existing deform which is locked to the shapekey values rather than actually editing the vertex. I do not want to change the basis because I already have set to default.
If you click the drop-down arrow in the Shape Keys panel there is an option for 'New Shape From Mix' - this creates a new shape key from the mix of all your existing shape keys and values.
Simply set your shape key 'values' to set 0.5 for the key you want to get the 'half-way' position of and select 'New Shape From Mix'. This will create a new shape key that produces that distortion when fully set.
You can use the same method to create a new shapekey from a mix of any amount of any number of your existing shape keys.