no, it should be fine.. i transplanted an autoflower after about the same time into plagron royal mix (which states an EC of up to 1.6, so also the mix that's heavily fertilized and meant for flowering)..
what i did was to first rinse out the soil with about 4 to 5 times the amount of water, so all the strong short-term nutrients are flushed out (to not cause any immediate burns), and put the seedling with the original starter-soil in it (so the roots aren't immediately exposed).. the other nutrients will be released over time, and i didn't need to feed them since..
it didn't seem to harm the plants at all, there were no signs of overfertilization or nutrient lockout or similar..