Learn Spanish (Latin America): Coloco los ratones aquí de manera que ustedes no tengan tensión. - I place the mice here so that you do not have tension.

The phrase de manera que can express either a purpose (so that) or a consequence (as a result). When it expresses a purpose or a goal, it triggers the subjunctive. Here, the speaker is placing the mice with the specific goal that the people won't experience tension, so tengan is required.

How would the meaning change if I used the indicative tienen?

If you say de manera que ustedes no tienen tensión, it changes from expressing a purpose to stating a fact about a consequence. It would translate closer to "I place the mice here, and as a result, you do not have tension." Using the indicative states what actually happens, while the subjunctive focuses on the intention behind the action.

Is ratones referring to animal mice or computer mice here?

Just like in English, ratones can mean both the animal and the computer device. Because the sentence mentions preventing tensión (likely muscle strain or ergonomic tension), this is almost certainly talking about setting up computer mice in a workspace.

Could I use poner instead of colocar?

Yes, poner is the most common word for to put or to place, and it would work perfectly here. Colocar is just slightly more precise, often used when positioning something carefully or in a specific arrangement, like setting up an ergonomic desk space.