I don't really understand your question. What do you mean by "concentrated perfume oil"? I Googled and found different things being sold under that name. But a fragrance oil for soap is concentrated fragrance that is soap safe and skin safe.
You can scent your soap with essential oils. Though some aren't skin safe, so do some research before you do. I don't understand why you want to turn an essential oil into a fragrance oil?
Absolutes and pure essential oils, or blends of these, can be used without dilution. Generally they are used at a smaller % per pound of oils in your recipe than fragrance oils. There are some online tools to help estimate usage rate, and you can test starting with the most conservative/smallest usage.
Soapmakers generally do not label pure essential oils or essential oil blends as "fragrance oils," even when diluted. Fragrance oils are defined as synthetically manufactured from a number of aroma chemicals, rather than composed of pure plant oils.
Concentrated perfume oils, blends of aromatic chemicals, or blends of essential oils with synthetic chemicals should only be used if the manufacturer has classified them all and individually safe for bath and body products, at a certain max percentage. If the oil you are using is sold as home or personal fragrance and does not have published information on usage in home-crafted bath products, I would not use it.
I've heard of at-home perfumers using pure chemical compounds like limonene and vanillin in their perfumes, so I'm sure it's possible to formulate your own fragrance oils, but I can't see it being very cost-effective. You'd have to buy hundreds of different chemicals, and find somewhere to store them - not ideal, to say the least!