2 kinds of fiberglass tape. One is for drywall. One is for alkaline environments. Big difference. A shower is a harsh environment. The expensive tape, alkaline-resistant, is the right thing to use. I believe it is the only product that has been approved by the TCNA. The other tape degrades, falls apart, does not hold the seams together, in the long term. Very few people mention this, anywhere. It is not common knowledge. When you go into a store, many of the "specialist" staff won't know. Even if they read the labels, and understand it all, they may tell you that the cheap one "works too". Yes, it works, initially, as it appears to hold the Hardi panels together, and if some aisle person is all of 22 years old, his sense of time-risk-proper- and all that is not to be trusted, assuming you want the installation to be done right, by standards recognized by industry associations.
Shower water can slide in behind any tile, even thought the grout looks intact and well attached. Also, grout itself is not waterproof, unless it is epoxy based grout. A shower a day keeps the wall moist inside, if there is any small amount of water getting in. Moist = mold grows. Smells bad, makes you sick, infects the whole house sometimes.
"Mud" is a cute word. Let's call it Portland-cement based product. Thinset is one.
"Mud" is a broad term. In drywall, it can refer to "compound".
"Mud" for some people can refer to the product known as mastic, which is an organic based material, not portland cement based. Organic material rots. When put under shower tiles, it is not up to TCNA standards. Mastic is good as a tile setting product, but not in showers.
Anyone can say, that this or that thing they do is a small thing in the big picture, and that what they are doing will work, and that the TCNA has only adopted a few things as the right thing to do....
Whether you use mastic in a shower,
whether you use mastic only on the screw holes,
whether you use the right or wrong fiberglass tape,
these are details, that may make a big difference
Or none at all. But there is no way to know in advance. I have no problem with a touch of mastic on a screw hole. Just don't use mastic to set all your tiles.
Honeysuckle, these are some of the reasons why you will have a hard time with the previous guy. It takes a lot of talk, a lot of explaining, just to say all of the above. Imagine how hard it will be to talk to someone who knows more than you do and won't listen to your new-found knowledge that is still quite limited. If you have already explained all this ten or twenty time before, it gets easy. Today is not a good day to teach the old guy new stuff.
If you unscrew the Hardi, then later when you put the vapor barrier in, you have to ensure that it is long enough to "drip into" the tub flange.
You may have one other option, an alternative to unscrewing it. That is, to paint a liquid trowelable shower membrane on it.
First, we need to see how the Hardi touches the tub edge. The "flange".
david