Not much. Linked "mass segregation" suggests that core's Iron content will be much higher than Iron content in other layers anyway, thus, we can expect crust, layer on which we live and from which we extract elements, to have roughly same composition. Perhaps iron ores are a bit more common, but change shouldn't have significant impact on development of civilisation.
Planet mass isn't significantly affected; as explained above, other layers are mostly unaffected, while core is made of Iron with Nickel on distant second. Iron has density of $7.8 \frac{g}{cm^3}$, Nickel has density of $ 8.9 \frac{g}{cm^3}$. Assuming that 1/3 of mass is contained in core (result of quick google search), by replacing 6% of its mass with Iron you are decreasing planet's mass by $ 0.3(3)*6\%*\frac{7.8}{8.9}\approx 1.7\% $
dropping planet's gravity to $9.64 \frac{m}{s^2}$ compared to real Earth's $9.81 \frac{m}{s^2}$. Sorry, here I made a mistake in previous version you are decreasing mass, not increasing as I previously wrote.
Magnetic field shouldn't be changed significantly either. Not only Iron is a dominant element contributing to core's physical properties, but cursory search suggests Iron and second main element: Nickel have similar properties.
All in all, I can't imagine any significant changes.