Looking through the Halo Archive really quick (which is the main source of game models that we use - link will be in the Blender thread that Blaze posted), no one's really made any adjustments to the Infinite undersuit in the way you're describing. The original Reach Spartan models are hosted there, however, so if you're looking for something like that then I'd honestly just say to stick with them.
Besides those, one alternative you could consider is using a Halo 5 undersuit base and then attaching the Infinite Mark V stuff to it, but that'd be more time-intensive and requires a bit more knowledge of how to reparent objects to rigs. One final option is Spartan Griffin's undersuit from Infinite's campaign, which is included with the latest version of Infinite Spartan Pack. I've seen armor setups using Griffin's suit as a base, and you could probably sculpt it to fit a more female figure.
One thing I'll say about the Reach and Infinite undersuits: in case you weren't already aware, they are not one single object. They're split up into different parts based on what's visible, i.e. the stomach area will be its own object, as will the elbows and knees. Keep that in mind should you decide to mess around with the Infinite setup. Halo 5's and Griffin's techsuits are one piece, however.
