Come to think of it, I did dig a hole next to a rose bush and buried a
couple of banana peels (potassium, etc) down there. I'm not really into
growing flowers, so if I needed a specific amendment, I probably wouldn't
know it.

Seem like you don't need to add any amendment to your garden yet.

Seem like if we need to add amendment to the soil where it is covered
in landscape fabric, we will have to open/remove the landscape fabric
partially or completely. This sounds like something that we need to
schedule it in advance (such as a plan like "I may need to remove the
landscape fabric after x years if a soil test indicates that the soil
is lack of something, and then I can put the landscape fabric back").

I am sure that this can be done. I just didn't think of this when I
put the landscape fabrics to my flower garden a couple years ago.
Without knowing this in advance and making a committment to do this, I
am now kind of surprised by the idea of removing and putting back the
landscape fabrics.

Honestly, I don't really have any better idea either. If I don't put
mulch on it, I will have to deal with a lot more weeds, and I may have
a hard time to remove weeds if they have formed solid root into the
soil. If I put mulch without landscape fabrics, the mulch will be
mixed with soil, and I will still need to deal with more weeds. If I
put mulch and landscape fabrics, I will have to remove/open landscape
fabrics to add amendment. Seem like I am better off sticking with
making as little change as possible; this means I should remove the
mulch that is infected with termintes (this is the minimum that I
should do), leave the landscape fabric there, and put fresh new mulch
(probably the kind that you use). Also order a long handle weeder to
remove weeds that manage to grow among the mulch. And worry about
adding amendment later.

This sounds like a plan.

Jay Chan