- if you do it , obviously, from your personal account/email address.
There are stricter rules for supervisor-level federal employees - higher-level administrators- than "regular" employees, but I'm almost positive that even supervisors can make donations.
Active participation in campaigns - fundraising, canvassing, speaking at public events, signing public letters that are displayed online or as full-page ads in newspapers, etc - is definitely forbidden for supervisor types- probably also a no-no for lower-level employees. Display of partisan political signs in offices is also forbidden.
I think that attendance at partisan political fund-raisers also may be a no-no, out I'm almost positive that attendance at political speeches is OK provided no fundraising is involved and you attend as a private citizen .
There was a brouhaha a few years back when Jon Stewart and Steve Colbert held that rally on the Mall. Some supervisor at some federal agency forbade his employees from attending. (I'm guessing that, since the event was going to be televised, the supervisor was worried that one of the employees would end up on camera). But, as I remember, everyone said he was wrong; the clear consensus was that federal employees had every right to attend.
All this applies to the "civil service"-type executive branch. (Probably applies to judicial branch, too).
I presume that employees of the legislative branch are allowed (even expected) to display their partisan selves.
In any case, you're not working for a federal contractor YET; so, unless your new employer refuses to hire anyone who ever had a political opinion in his or her life (which would be bizarre), you should be able to donate NOW, no matter what.
You could check the rules for federal employees through the Office of Personnel Management to be sure. But FWIW I'm almost positive that donations are OK even for federal employees, which means that it should also be OK for federal contractors.
PS. Also, you'll have to put off running for office yourself.