Can a Ligularia be spilt?
Yes, lift the entire plant, taking care not to damage the crown.
The Ligularia will many times have little off shoots next the main crown.
These small off shoots can also be removed and new plantings started.
Keep the plants out of the ground as little time as possible.
https://www.gardeningknowhow.com/ornamental/flowers/ligularia/ligularia-ragwort-flower.htm
We had an unusual freeze here in Houston (24) and my Ligularia were frozen and turned brown. It was obvious those leaves would not come back, but are the roots OK? Will they bloom again? We are back to 70 degrees.
Your plant should grow back just fine. Ligularia can be cultivated in regions as cold as zone 4, where the ground is frozen for most of the winter. In these regions the leaves die back but the root survives and sprouts again the next spring. Sooner or later, your plant will grow back.
we have great luck growing ligularia...our yard is full and we love them. People stop and stare because they have never seen this plant in Iowa. Does it come in any color flower besides gold?
No, they have a yellow or gold coloration.
https://www.gardeningknowhow.com/ornamental/flowers/ligularia/ligularia-ragwort-flower.htm
This well established plant has now "raised" itself several inches above the garden surface level. Should I replant it lower? if not, should I be worried?
This article tells how to care for them:
https://www.gardeningknowhow.com/ornamental/flowers/ligularia/ligularia-ragwort-flower.htm
What is the best type of fertilizer to use? After flowering am I best to cut back the flowering stem or not? Do i cut back the dead leaves as well?
Yes, you can cut back flowering stems as they finish blooming and cut back any dead foliage as well. Apply a balanced, slow release fertilizer, such as 10-10-10, once a year in spring.
Here is more:
https://www.gardeningknowhow.com/ornamental/flowers/ligularia/ligularia-ragwort-flower.htm