If you use something like TA+WS, it only calculates damage based on your gear/stats one time. When you pop TA, ffxi calculates nothing. When your WS then fires and (I suppose when) you see the message "xxx readies weapon skill," at that time is when the calculation occurs.
http://wiki.ffxiclop...on_Skill_Damage
WD = ( D +
fSTR +
WSC) * fTP +
AGI
Any AGI that you have on at the time will be calculated where it shows 'agi' in red. Any WS mods will be calculated in the formula at 'wsc', in blue (these are your weaponskill mods. IE for Dancing Edge, the mods are dex and chr, so that's calculated here). Any Str you have on can give you a boost, and this is calculated at 'fStr' shown in green. 'D' is the base damage of your weapon. fTP is a type of WS mod based on your TP. 'WD' means Weaponskill Damage. After 'WD' is calculated based on these stats, the WD is then multiplied against (a function of) your attack, and accuracy.
So long story short, no, you can't swap multiple times to increase your damage further.