Also called locked stitches.
Modified Tunisian simple stitch
Insert your hook under the front vertical bar AND upward under the top horizontal bar of the RetP chain, yarn over and pull up a loop.
What difference does it make compared to the basic Tss? The modified Tss looks different on the front and back of the work. I personally find the back side much neater with the modified Tss. Which makes it one of my favorite stitches.
Modified Tunisian knit stitch
Insert your hook in between the front and back vertical bars, from front to back, through the work AND through the RetP chain, under the top and back horizontal bars and above the bottom horizontal bar, yarn over and pull up a loop.
What difference does it make compared to the basic Tks? It looks different. But beyond the pure visual aspect, the modified Tks makes a slightly flatter fabric.
Modified Tunisian full stitch
Insert your hook through the RetP chain in between 2 stitches, under the top and back horizontal bars and above the bottom horizontal bar, yarn over and pull up a loop.
Stitches being picked up in between stitches from the previous row (just like the basic Tfs), your work will lean to the right (1) if the first stitch is systematically picked up between the edge stitch and the next stitch, or to the left (2) if the first stitch is systematically picked up between the 2 stitches after the edge stitch. (or the other way for left-handed crocheters).
Modified Tunisian reverse stitch
In theory, if we stick to the same logic, a modified Trs is made by inserting the hook under the back vertical bar AND under the back horizontal bar (back ridge) of the RetP chain. In practice, this is arduous to make and I personally find little interest in this stitch compared to the effort invested to make it.