during recruiting informing of a redshirt clears any previously offered promises. Be aware however that it also carries an immediate (ie does not wait until the next 3 hour cycle to take effect) negative impact. You can then inform of No redshirt and clear the redshirt, but some of the negative reaction remains.
So if the recruit is not all that heavily in to you doing this can cause them to move from considering to not considering. If you want to sign the kid, do the offer first, and let it propagate at next cycle along with a minimal amount of effort (1 or 2 HVs). Then use the redshirt inform/uninform switcheroo to clear the promises, and at next cycle you'll get a message thanking you for not redshirting and should still be considered.
Also be aware that if you do this you will not be able to redshirt the player without a massive WE drop (like to 1). If you plan to redshirt him you'd have to either leave the inform on (and send a bit more effort to compensate) or re-inform again before signing. Each inform/uninform is its own instance, so you'd get negative value again, but at least the player would be reset to ok with redshirt (*note that in many cases once the season begins if you do redshirt these players the message reply you get might sound negative, but as long as you informed and he still signed he will take redshirt with no WE drop.)