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If the plant has gotten leggy and it's receiving good filtered light, it is likely just aging and needs to be pruned and cut back.

You can start new plants with the cuttings if you would like. Cut it back to a leaf cluster on the branches of the plant.
If the plant has not been repotted in awhile, it may be a good time to move the plant up 1 size and refresh the soil. Use a good quality potting mix and make sure the pot has an adequate drainage hole.

You can add an all purpose slow release fertilizer to the soil.

https://www.gardeningknowhow.com/houseplants/purple-passion-plant/purple-passion-houseplants.htm

Yes, you can prune the plant back to any size you prefer. If you cut the "leg" back to maybe the fourth or fifth leaf from the base, it will most likely grow two stems from that point. Or, you can leave it longer and use it as a hanging or trailing plant.

Your local nursery will know best on how to care for these in your area. The requirements will be different depending on where you are located, so I would trust your local sources on the care of these.

Rules vary state by state. The federal government does not list velvetleaf as a prohibited species or noxious weed. Several states have listed it as a regulated Noxious Weed, Colorado, Iowa, Oregon and Washington. Seeds can not be sold there. There are also subclasses to noxious weeds with varying degrees of control/removal required. There are also state "non-regulated" noxious weed lists which means control or removal is not mandated but recommended. Very few plants are listed as Federally banned. Most often, economic concerns drive decisions to ban species such as plants that reduce crop yields or that contaminate seed operations. A plant that is simply a nuisance probably won't rise to the level whereby the sale of seed or plants is prohibited. The following website lists all the Noxious Weeds as designated by the US government and individual states. https://plants.sc.egov.usda.gov/java/noxiousDriver#federal