Has been observed any changes in the real sun´s size on ocassion of the 1979 solar storm event ? (after and before)
No, no such changes have been observed. Laclare et al. (1996) summarize various published solar diameter data from observations made between 1970 and 1995. Here's Figure 6 from their paper.
As you can see (and as Laclare et al. point out), solar semi-diameter has shown no significant variation during the measurement periods. Given their deviation from the other data sets, the Wittmann data seem rather suspect, but even they show absolutely no change between the 1972 and 1981 data points. In short, none of these data are consistent with the notion that solar diameter changed in 1979.
Laclare, F., Delmas, C., Coin, J. P., & Irbah, A. (1996). Measurements and variations of the solar diameter. Solar Physics, 166(2), 211-229.