If one did not prepare sufficient clothes to wear during the week of Tish'ah BeAb, one may not prepare clothes on Shabbath Hazon the way one does during the week. In other words, one may not wear the items for an hour and take them off and then do the same again, until one has prepared enough. This would be preparing on Shabbath for a weekday, which is not permitted.
Instead, one should wear the laundered clothes on Shabbath at night and remove them, and then wear different clothes during the day. Those clothes should not be changed during the day without a reason. If a person wishes to sleep and would, therefore, ordinarily remove his shirt, he may then wear another shirt when he wakes up.
All this applies to the kind of clothes that a person would wear on Shabbath. However, one may not take one's freshly laundered weekday clothes and prepare them in this manner on Shabbath, because this would be considered preparing on Shabbath for a weekday.
(See Ben Ish Hai, 1st year, Debarim, Oth 6. Maamar Mordekhai [Eliyahu], Haggim, 25: 82, 83)
Tish'ah BeAb, Tishah B'av, Shabbat Chazon, Shabbath Hazon,