I don't know anything about the laws limiting transfer of fissile material and may violate issues with NATO membership. I'm not seeing the upside for Sweden to do any of this.
And from a quick search makes it sound like decommissioning of Ågestaverket began in 2020 and should be done in 2025. So the plant would need to be, essentially, rebuilt.
Next, the nuclear program was shut down in 1961 because they didn't have any Pu-240 to refine into Pu-247. Finally, when the program did exist, they had to get their heavy water from Norway. Heavy water allows them to use yellow cake directly for fissile material, but they still use light water but need an enrichment program. So, technically it's a long way still.
They could eventually spin it up, but would take longer than the months you first mention. Technical and material issues exist between yellow cake and weapons grade fissile material that the Ukrainian may not have access to (heavy water or plutonium). Even if they do, transforming their current civilian system would take several years optimistically.
Ultimately, that's my biggest issue is time. It's not months but years.