We must consider the practical realities of the time in which the Rambam (and many other important rabbinic figures) lived.
There were no airplanes. Travel by boat was expensive, difficult, and dangerous. Travel by land was not much easier, and usually not much less dangerous.
If a Jew managed to make it to the Holy Land, and survived the trip, he wasn't coming for a two week vacation, or even a year of learning in yeshiva. At the very least, he was there for an open-ended stay.
Now we can see why Rambam, and others, don't discuss the difference between "aliyah" and just coming for a visit. There was no practical difference in their times!
I highly recommend two excellent sefarim on this topic.
Eim HaBanim Smeicha and MeAfar Kumi
I know that Eim HaBanim Smeicha is available in English, and I read recently that an English translation of MeAfar Kumi is coming out soon, if it isn't out already.
Both of these sefarim bring an overwhelming multitude of sources, which prove that living in Eretz Yisrael is always a positive commandment, and binding obligation.
Like any other positive commandment, there are times when one may be temporarily exempt.
However, being born and raised in Exile, in and of itself, is not an exemption.
Thefore, the answer to the original question is NO. One cannot conditionally make aliyah, because a Jew is already obligated to live in Eretz Yisrael.
Regarding the post high-school programs for English speakers in Israel, which are very popular among English speaking Exile Jews:
In general, they are wonderful programs. In addition to a high level of learning, these programs give young Jewish men and women an opportunity to experience their homeland, and hopefully they will choose to fulfill their obligation of living in it.
If these students choose to leave Eretz Yisrael after one or two years, we can be "m'lamed zchus" in the following ways:
they are going to gather their belongings together and return home to Israel.
they are going to get a specific type of education, which they cannot get in Israel, and which will enable them to return home to Israel and make a living in the future.
they are going to find a spouse, they assume (rightly or not) that they will be more compatible with another Exile Jew, and will return once they are married.
they have an immediate family member who cannot care for him/herself, and they are the best equipped to care for this individual.
they have some other very specific Torah obligation that only they can do while in Exile.
All of the above reasons are valid for a TEMPORARY absence from Eretz Yisrael.
Even if one spends many years, or G-d forbid his/her whole life in Exile, one must at the very least consider his/her stay there temporary, and actively work towards fulfilling the mitzvah of living in the Holy Land.
Again, sources for the above comments can be found in Eim Habanim Smeichah and MeAfar Kumi, which in turn cite a very wide variety of halachic sources.
