answer:Oh you could probably do it without sewing at all. Or very minimal. There is this stuff used to reinforce zippers its fabric strips wrapped around a piece of cardboard and the strips are folded so it opens to various widths. All sorts of different colors you could use a simple or even decorative stitch to hold in place after pinning it they way you desire for the trim. Other options include fabric markers. Seems somewhat cheesy. But there are some good fabric paints just tape off the area and put something cardboard inbetween front and back you can test this on some old clothing. Another option is bleaching the area, this technique is widely used with tiedyers so visit a website and practice it before you give it a shot on the real thing. As to the v in the turtleneck it’s difficulty might lay in fabric type and construction but you could do something a simple as cut not below the start of the tunic and gets some fabric glue or fusable material. If the neck gets floppy and is a flod type construction you may be able to insert cardboard collars, use starch or stiffener, which would be less permanent or reinforce the back with a stiffer fusing see quilting notions or tshirt embroadiary packets… To shorten the bottom will be easier you can measure twice cut, fabric mats and rollers are best for this but you can make do. Measure pin and seam. all materials can be found in a joanns or michaels or sometimes even walmart.