The first question is already answered but you ask for more details on borer and muktze. Overall they do not represent obstacles to using such a knife.
There is no issue of borer when selecting the good from the bad, in this case the tool you want from the others, with the hand, right before use. Shemirat Shabbat KeHilchata (3:27) notes it is permitted to select an article which one wishes to use at present from articles of the same type which come in different sizes or colors and do not all have an identical use.
Regarding muktze, one may move an object (to use it, or for its space) if it is used with equal (or more) frequency for performing both permitted and prohibited activities (Shemirat Shabbat KeHilchata 20:80). This is a kli shemelachto l'issur, see SA OC 308:3 and following.
However note that one should not use these objects if one has available an article whose use is not restricted (SSK 20:8) or for a non-Jew.
I would also note the Shemirat Shabbat KeHilchata (20:81) explicitely discusses a penknife which appears to be similar to a Swiss knife (i.e., a tool with multiple blades, some of which might be useful for a permitted use on Shabbat, others not)
A penknife sometimes has fixed attachments which may not be used on
Shabbath, such as scissors or a nail-file. Even if one is particular
not to use these attachments for any other than their intended
purpose, one may move the penknife in order to use its blade. One must
not, however, open those attachments that it is forbidden to use.