Yes, you can – and actually you should bathe before taking pachkhan of ekasana, if it is practically possible for you.

Simple order (ideal way):

1. Wake up
2. Do snan (bath) and get ready in clean clothes
3. Do morning vidhi / samayik / pratikraman as per your practice
4. Then stand and take pachkhan for ekasana (before food and usually before or near sunrise)
5. Later, take your one meal in one sitting, before sunset

Bathing is for sharir shuddhi (outer purity), which supports bhav shuddhi (inner purity) when you take any vow like ekasana.

If due to health, travel, or some genuine reason you cannot bathe, pachkhan is still mainly about bhav and niyam. In such a case, you may:

• At least wash hands, feet, face, and mouth properly
• Wear as clean clothes as you can
• Then take pachkhan with pure intention

For more detailed guidance on ekasana and pachkhan, you can read here